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@@ -3279,8 +3279,412 @@
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</literallayout>
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</para>
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</section>
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+</section>
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+
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+<section id='profile-manual-blktrace'>
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+ <title>blktrace</title>
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+
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+ <para>
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+ blktrace is a tool for tracing and reporting low-level disk I/O.
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+ blktrace provides the tracing half of the equation; its output can
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+ be piped into the blkparse program, which renders the data in a
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+ human-readable form and does some basic analysis:
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+ </para>
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+
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+ <section id='blktrace-setup'>
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+ <title>Setup</title>
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+
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+ <para>
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+ For this section, we'll assume you've already performed the
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+ basic setup outlined in the
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+ "<link linkend='profile-manual-general-setup'>General Setup</link>"
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+ section.
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+ </para>
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+
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+ <para>
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+ blktrace is an application that runs on the target system.
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+ You can run the entire blktrace and blkparse pipeline on the
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+ target, or you can run blktrace in 'listen' mode on the target
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+ and have blktrace and blkparse collect and analyze the data on
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+ the host (see the
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+ "<link linkend='using-blktrace-remotely'>Using blktrace Remotely</link>"
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+ section below).
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+ For the rest of this section we assume you've ssh'ed to the
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+ host and will be running blkrace on the target.
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+ </para>
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+ </section>
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+
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+ <section id='blktrace-basic-usage'>
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+ <title>Basic Usage</title>
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+
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+ <para>
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+ To record a trace, simply run the 'blktrace' command, giving it
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+ the name of the block device you want to trace activity on:
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+ <literallayout class='monospaced'>
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+ root@crownbay:~# blktrace /dev/sdc
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+ </literallayout>
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+ In another shell, execute a workload you want to trace.
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+ <literallayout class='monospaced'>
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+ root@crownbay:/media/sdc# rm linux-2.6.19.2.tar.bz2; wget <ulink url='http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2'>http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2</ulink>; sync
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+ Connecting to downloads.yoctoproject.org (140.211.169.59:80)
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+ linux-2.6.19.2.tar.b 100% |*******************************| 41727k 0:00:00 ETA
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+ </literallayout>
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+ Press Ctrl-C in the blktrace shell to stop the trace. It will
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+ display how many events were logged, along with the per-cpu file
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+ sizes (blktrace records traces in per-cpu kernel buffers and
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+ simply dumps them to userspace for blkparse to merge and sort
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+ later).
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+ <literallayout class='monospaced'>
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+ ^C=== sdc ===
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+ CPU 0: 7082 events, 332 KiB data
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+ CPU 1: 1578 events, 74 KiB data
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+ Total: 8660 events (dropped 0), 406 KiB data
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+ </literallayout>
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+ If you examine the files saved to disk, you see multiple files,
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+ one per CPU and with the device name as the first part of the
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+ filename:
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+ <literallayout class='monospaced'>
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+ root@crownbay:~# ls -al
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+ drwxr-xr-x 6 root root 1024 Oct 27 22:39 .
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+ drwxr-sr-x 4 root root 1024 Oct 26 18:24 ..
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+ -rw-r--r-- 1 root root 339938 Oct 27 22:40 sdc.blktrace.0
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+ -rw-r--r-- 1 root root 75753 Oct 27 22:40 sdc.blktrace.1
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+ </literallayout>
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+ To view the trace events, simply invoke 'blkparse' in the
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+ directory containing the trace files, giving it the device name
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+ that forms the first part of the filenames:
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+ <literallayout class='monospaced'>
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+ root@crownbay:~# blkparse sdc
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+
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+ 8,32 1 1 0.000000000 1225 Q WS 3417048 + 8 [jbd2/sdc-8]
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+ 8,32 1 2 0.000025213 1225 G WS 3417048 + 8 [jbd2/sdc-8]
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+ 8,32 1 3 0.000033384 1225 P N [jbd2/sdc-8]
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+ 8,32 1 4 0.000043301 1225 I WS 3417048 + 8 [jbd2/sdc-8]
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+ 8,32 1 0 0.000057270 0 m N cfq1225 insert_request
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+ 8,32 1 0 0.000064813 0 m N cfq1225 add_to_rr
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+ 8,32 1 5 0.000076336 1225 U N [jbd2/sdc-8] 1
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+ 8,32 1 0 0.000088559 0 m N cfq workload slice:150
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+ 8,32 1 0 0.000097359 0 m N cfq1225 set_active wl_prio:0 wl_type:1
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+ 8,32 1 0 0.000104063 0 m N cfq1225 Not idling. st->count:1
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+ 8,32 1 0 0.000112584 0 m N cfq1225 fifo= (null)
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+ 8,32 1 0 0.000118730 0 m N cfq1225 dispatch_insert
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+ 8,32 1 0 0.000127390 0 m N cfq1225 dispatched a request
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+ 8,32 1 0 0.000133536 0 m N cfq1225 activate rq, drv=1
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+ 8,32 1 6 0.000136889 1225 D WS 3417048 + 8 [jbd2/sdc-8]
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+ 8,32 1 7 0.000360381 1225 Q WS 3417056 + 8 [jbd2/sdc-8]
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+ 8,32 1 8 0.000377422 1225 G WS 3417056 + 8 [jbd2/sdc-8]
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+ 8,32 1 9 0.000388876 1225 P N [jbd2/sdc-8]
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+ 8,32 1 10 0.000397886 1225 Q WS 3417064 + 8 [jbd2/sdc-8]
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+ 8,32 1 11 0.000404800 1225 M WS 3417064 + 8 [jbd2/sdc-8]
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+ 8,32 1 12 0.000412343 1225 Q WS 3417072 + 8 [jbd2/sdc-8]
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+ 8,32 1 13 0.000416533 1225 M WS 3417072 + 8 [jbd2/sdc-8]
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+ 8,32 1 14 0.000422121 1225 Q WS 3417080 + 8 [jbd2/sdc-8]
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+ 8,32 1 15 0.000425194 1225 M WS 3417080 + 8 [jbd2/sdc-8]
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+ 8,32 1 16 0.000431968 1225 Q WS 3417088 + 8 [jbd2/sdc-8]
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+ 8,32 1 17 0.000435251 1225 M WS 3417088 + 8 [jbd2/sdc-8]
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+ 8,32 1 18 0.000440279 1225 Q WS 3417096 + 8 [jbd2/sdc-8]
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+ 8,32 1 19 0.000443911 1225 M WS 3417096 + 8 [jbd2/sdc-8]
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+ 8,32 1 20 0.000450336 1225 Q WS 3417104 + 8 [jbd2/sdc-8]
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+ 8,32 1 21 0.000454038 1225 M WS 3417104 + 8 [jbd2/sdc-8]
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+ 8,32 1 22 0.000462070 1225 Q WS 3417112 + 8 [jbd2/sdc-8]
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+ 8,32 1 23 0.000465422 1225 M WS 3417112 + 8 [jbd2/sdc-8]
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+ 8,32 1 24 0.000474222 1225 I WS 3417056 + 64 [jbd2/sdc-8]
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+ 8,32 1 0 0.000483022 0 m N cfq1225 insert_request
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+ 8,32 1 25 0.000489727 1225 U N [jbd2/sdc-8] 1
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+ 8,32 1 0 0.000498457 0 m N cfq1225 Not idling. st->count:1
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+ 8,32 1 0 0.000503765 0 m N cfq1225 dispatch_insert
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+ 8,32 1 0 0.000512914 0 m N cfq1225 dispatched a request
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+ 8,32 1 0 0.000518851 0 m N cfq1225 activate rq, drv=2
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+ .
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+ .
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+ .
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+ 8,32 0 0 58.515006138 0 m N cfq3551 complete rqnoidle 1
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+ 8,32 0 2024 58.516603269 3 C WS 3156992 + 16 [0]
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+ 8,32 0 0 58.516626736 0 m N cfq3551 complete rqnoidle 1
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+ 8,32 0 0 58.516634558 0 m N cfq3551 arm_idle: 8 group_idle: 0
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+ 8,32 0 0 58.516636933 0 m N cfq schedule dispatch
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+ 8,32 1 0 58.516971613 0 m N cfq3551 slice expired t=0
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+ 8,32 1 0 58.516982089 0 m N cfq3551 sl_used=13 disp=6 charge=13 iops=0 sect=80
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+ 8,32 1 0 58.516985511 0 m N cfq3551 del_from_rr
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+ 8,32 1 0 58.516990819 0 m N cfq3551 put_queue
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+
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+ CPU0 (sdc):
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+ Reads Queued: 0, 0KiB Writes Queued: 331, 26,284KiB
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+ Read Dispatches: 0, 0KiB Write Dispatches: 485, 40,484KiB
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+ Reads Requeued: 0 Writes Requeued: 0
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+ Reads Completed: 0, 0KiB Writes Completed: 511, 41,000KiB
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+ Read Merges: 0, 0KiB Write Merges: 13, 160KiB
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+ Read depth: 0 Write depth: 2
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+ IO unplugs: 23 Timer unplugs: 0
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+ CPU1 (sdc):
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+ Reads Queued: 0, 0KiB Writes Queued: 249, 15,800KiB
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+ Read Dispatches: 0, 0KiB Write Dispatches: 42, 1,600KiB
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+ Reads Requeued: 0 Writes Requeued: 0
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+ Reads Completed: 0, 0KiB Writes Completed: 16, 1,084KiB
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+ Read Merges: 0, 0KiB Write Merges: 40, 276KiB
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+ Read depth: 0 Write depth: 2
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+ IO unplugs: 30 Timer unplugs: 1
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+
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+ Total (sdc):
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+ Reads Queued: 0, 0KiB Writes Queued: 580, 42,084KiB
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+ Read Dispatches: 0, 0KiB Write Dispatches: 527, 42,084KiB
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+ Reads Requeued: 0 Writes Requeued: 0
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+ Reads Completed: 0, 0KiB Writes Completed: 527, 42,084KiB
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+ Read Merges: 0, 0KiB Write Merges: 53, 436KiB
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+ IO unplugs: 53 Timer unplugs: 1
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+
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+ Throughput (R/W): 0KiB/s / 719KiB/s
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+ Events (sdc): 6,592 entries
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+ Skips: 0 forward (0 - 0.0%)
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+ Input file sdc.blktrace.0 added
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+ Input file sdc.blktrace.1 added
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+ </literallayout>
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+ The report shows each event that was found in the blktrace data,
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+ along with a summary of the overall block I/O traffic during
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+ the run. You can look at the
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+ <ulink url='http://linux.die.net/man/1/blkparse'>blkparse</ulink>
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+ manpage to learn the
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+ meaning of each field displayed in the trace listing.
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+ </para>
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+
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+ <section id='blktrace-live-mode'>
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+ <title>Live Mode</title>
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+
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+ <para>
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+ blktrace and blkparse are designed from the ground up to
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+ be able to operate together in a 'pipe mode' where the
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+ stdout of blktrace can be fed directly into the stdin of
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+ blkparse:
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+ <literallayout class='monospaced'>
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+ root@crownbay:~# blktrace /dev/sdc -o - | blkparse -i -
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+ </literallayout>
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+ This enables long-lived tracing sessions to run without
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+ writing anything to disk, and allows the user to look for
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+ certain conditions in the trace data in 'real-time' by
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+ viewing the trace output as it scrolls by on the screen or
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+ by passing it along to yet another program in the pipeline
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+ such as grep which can be used to identify and capture
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+ conditions of interest.
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+ </para>
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+
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+ <para>
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+ There's actually another blktrace command that implements
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+ the above pipeline as a single command, so the user doesn't
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+ have to bother typing in the above command sequence:
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+ <literallayout class='monospaced'>
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+ root@crownbay:~# btrace /dev/sdc
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+ </literallayout>
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+ </para>
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+ </section>
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+
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+ <section id='using-blktrace-remotely'>
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+ <title>Using blktrace Remotely</title>
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+
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+ <para>
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+ Because blktrace traces block I/O and at the same time
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+ normally writes its trace data to a block device, and
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+ in general because it's not really a great idea to make
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+ the device being traced the same as the device the tracer
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+ writes to, blktrace provides a way to trace without
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+ perturbing the traced device at all by providing native
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+ support for sending all trace data over the network.
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+ </para>
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+
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+ <para>
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+ To have blktrace operate in this mode, start blktrace on
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+ the target system being traced with the -l option, along with
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+ the device to trace:
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+ <literallayout class='monospaced'>
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+ root@crownbay:~# blktrace -l /dev/sdc
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+ server: waiting for connections...
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+ </literallayout>
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+ On the host system, use the -h option to connect to the
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+ target system, also passing it the device to trace:
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+ <literallayout class='monospaced'>
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+ $ blktrace -d /dev/sdc -h 192.168.1.43
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+ blktrace: connecting to 192.168.1.43
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+ blktrace: connected!
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+ </literallayout>
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+ On the target system, you should see this:
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+ <literallayout class='monospaced'>
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+ server: connection from 192.168.1.43
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+ </literallayout>
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+ In another shell, execute a workload you want to trace.
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+ <literallayout class='monospaced'>
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+ root@crownbay:/media/sdc# rm linux-2.6.19.2.tar.bz2; wget <ulink url='http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2'>http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2</ulink>; sync
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+ Connecting to downloads.yoctoproject.org (140.211.169.59:80)
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+ linux-2.6.19.2.tar.b 100% |*******************************| 41727k 0:00:00 ETA
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+ </literallayout>
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+ When it's done, do a Ctrl-C on the host system to
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+ stop the trace:
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+ <literallayout class='monospaced'>
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+ ^C=== sdc ===
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+ CPU 0: 7691 events, 361 KiB data
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+ CPU 1: 4109 events, 193 KiB data
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+ Total: 11800 events (dropped 0), 554 KiB data
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+ </literallayout>
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+ On the target system, you should also see a trace
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+ summary for the trace just ended:
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+ <literallayout class='monospaced'>
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+ server: end of run for 192.168.1.43:sdc
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+ === sdc ===
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+ CPU 0: 7691 events, 361 KiB data
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+ CPU 1: 4109 events, 193 KiB data
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+ Total: 11800 events (dropped 0), 554 KiB data
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+ </literallayout>
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+ The blktrace instance on the host will save the target
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+ output inside a hostname-timestamp directory:
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+ <literallayout class='monospaced'>
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+ $ ls -al
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+ drwxr-xr-x 10 root root 1024 Oct 28 02:40 .
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+ drwxr-sr-x 4 root root 1024 Oct 26 18:24 ..
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+ drwxr-xr-x 2 root root 1024 Oct 28 02:40 192.168.1.43-2012-10-28-02:40:56
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+ </literallayout>
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+ cd into that directory to see the output files:
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+ <literallayout class='monospaced'>
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+ $ ls -l
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+ -rw-r--r-- 1 root root 369193 Oct 28 02:44 sdc.blktrace.0
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+ -rw-r--r-- 1 root root 197278 Oct 28 02:44 sdc.blktrace.1
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+ </literallayout>
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+ And run blkparse on the host system using the device name:
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+ <literallayout class='monospaced'>
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+ $ blkparse sdc
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+
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+ 8,32 1 1 0.000000000 1263 Q RM 6016 + 8 [ls]
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+ 8,32 1 0 0.000036038 0 m N cfq1263 alloced
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+ 8,32 1 2 0.000039390 1263 G RM 6016 + 8 [ls]
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+ 8,32 1 3 0.000049168 1263 I RM 6016 + 8 [ls]
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+ 8,32 1 0 0.000056152 0 m N cfq1263 insert_request
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+ 8,32 1 0 0.000061600 0 m N cfq1263 add_to_rr
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+ 8,32 1 0 0.000075498 0 m N cfq workload slice:300
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+ .
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+ .
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+ .
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+ 8,32 0 0 177.266385696 0 m N cfq1267 arm_idle: 8 group_idle: 0
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+ 8,32 0 0 177.266388140 0 m N cfq schedule dispatch
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+ 8,32 1 0 177.266679239 0 m N cfq1267 slice expired t=0
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+ 8,32 1 0 177.266689297 0 m N cfq1267 sl_used=9 disp=6 charge=9 iops=0 sect=56
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+ 8,32 1 0 177.266692649 0 m N cfq1267 del_from_rr
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+ 8,32 1 0 177.266696560 0 m N cfq1267 put_queue
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+
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+ CPU0 (sdc):
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+ Reads Queued: 0, 0KiB Writes Queued: 270, 21,708KiB
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+ Read Dispatches: 59, 2,628KiB Write Dispatches: 495, 39,964KiB
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+ Reads Requeued: 0 Writes Requeued: 0
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+ Reads Completed: 90, 2,752KiB Writes Completed: 543, 41,596KiB
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+ Read Merges: 0, 0KiB Write Merges: 9, 344KiB
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+ Read depth: 2 Write depth: 2
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+ IO unplugs: 20 Timer unplugs: 1
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+ CPU1 (sdc):
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+ Reads Queued: 688, 2,752KiB Writes Queued: 381, 20,652KiB
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+ Read Dispatches: 31, 124KiB Write Dispatches: 59, 2,396KiB
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+ Reads Requeued: 0 Writes Requeued: 0
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+ Reads Completed: 0, 0KiB Writes Completed: 11, 764KiB
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+ Read Merges: 598, 2,392KiB Write Merges: 88, 448KiB
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+ Read depth: 2 Write depth: 2
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+ IO unplugs: 52 Timer unplugs: 0
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+
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+ Total (sdc):
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+ Reads Queued: 688, 2,752KiB Writes Queued: 651, 42,360KiB
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+ Read Dispatches: 90, 2,752KiB Write Dispatches: 554, 42,360KiB
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+ Reads Requeued: 0 Writes Requeued: 0
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+ Reads Completed: 90, 2,752KiB Writes Completed: 554, 42,360KiB
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+ Read Merges: 598, 2,392KiB Write Merges: 97, 792KiB
|
|
|
+ IO unplugs: 72 Timer unplugs: 1
|
|
|
+
|
|
|
+ Throughput (R/W): 15KiB/s / 238KiB/s
|
|
|
+ Events (sdc): 9,301 entries
|
|
|
+ Skips: 0 forward (0 - 0.0%)
|
|
|
+ </literallayout>
|
|
|
+ You should see the trace events and summary just as
|
|
|
+ you would have if you'd run the same command on the target.
|
|
|
+ </para>
|
|
|
+ </section>
|
|
|
+
|
|
|
+ <section id='tracing-block-io-via-ftrace'>
|
|
|
+ <title>Tracing Block I/O via 'ftrace'</title>
|
|
|
+
|
|
|
+ <para>
|
|
|
+ It's also possible to trace block I/O using only
|
|
|
+ <link linkend='the-trace-events-subsystem'>trace events subsystem</link>,
|
|
|
+ which can be useful for casual tracing
|
|
|
+ if you don't want bother dealing with the userspace tools.
|
|
|
+ </para>
|
|
|
+
|
|
|
+ <para>
|
|
|
+ To enable tracing for a given device, use
|
|
|
+ /sys/block/xxx/trace/enable, where xxx is the device name.
|
|
|
+ This for example enables tracing for /dev/sdc:
|
|
|
+ <literallayout class='monospaced'>
|
|
|
+ root@crownbay:/sys/kernel/debug/tracing# echo 1 > /sys/block/sdc/trace/enable
|
|
|
+ </literallayout>
|
|
|
+ Once you've selected the device(s) you want to trace,
|
|
|
+ selecting the 'blk' tracer will turn the blk tracer on:
|
|
|
+ <literallayout class='monospaced'>
|
|
|
+ root@crownbay:/sys/kernel/debug/tracing# cat available_tracers
|
|
|
+ blk function_graph function nop
|
|
|
|
|
|
+ root@crownbay:/sys/kernel/debug/tracing# echo blk > current_tracer
|
|
|
+ </literallayout>
|
|
|
+ Execute the workload you're interested in:
|
|
|
+ <literallayout class='monospaced'>
|
|
|
+ root@crownbay:/sys/kernel/debug/tracing# cat /media/sdc/testfile.txt
|
|
|
+ </literallayout>
|
|
|
+ And look at the output (note here that we're using
|
|
|
+ 'trace_pipe' instead of trace to capture this trace -
|
|
|
+ this allows us to wait around on the pipe for data to
|
|
|
+ appear):
|
|
|
+ <literallayout class='monospaced'>
|
|
|
+ root@crownbay:/sys/kernel/debug/tracing# cat trace_pipe
|
|
|
+ cat-3587 [001] d..1 3023.276361: 8,32 Q R 1699848 + 8 [cat]
|
|
|
+ cat-3587 [001] d..1 3023.276410: 8,32 m N cfq3587 alloced
|
|
|
+ cat-3587 [001] d..1 3023.276415: 8,32 G R 1699848 + 8 [cat]
|
|
|
+ cat-3587 [001] d..1 3023.276424: 8,32 P N [cat]
|
|
|
+ cat-3587 [001] d..2 3023.276432: 8,32 I R 1699848 + 8 [cat]
|
|
|
+ cat-3587 [001] d..1 3023.276439: 8,32 m N cfq3587 insert_request
|
|
|
+ cat-3587 [001] d..1 3023.276445: 8,32 m N cfq3587 add_to_rr
|
|
|
+ cat-3587 [001] d..2 3023.276454: 8,32 U N [cat] 1
|
|
|
+ cat-3587 [001] d..1 3023.276464: 8,32 m N cfq workload slice:150
|
|
|
+ cat-3587 [001] d..1 3023.276471: 8,32 m N cfq3587 set_active wl_prio:0 wl_type:2
|
|
|
+ cat-3587 [001] d..1 3023.276478: 8,32 m N cfq3587 fifo= (null)
|
|
|
+ cat-3587 [001] d..1 3023.276483: 8,32 m N cfq3587 dispatch_insert
|
|
|
+ cat-3587 [001] d..1 3023.276490: 8,32 m N cfq3587 dispatched a request
|
|
|
+ cat-3587 [001] d..1 3023.276497: 8,32 m N cfq3587 activate rq, drv=1
|
|
|
+ cat-3587 [001] d..2 3023.276500: 8,32 D R 1699848 + 8 [cat]
|
|
|
+ </literallayout>
|
|
|
+ And this turns off tracing for the specified device:
|
|
|
+ <literallayout class='monospaced'>
|
|
|
+ root@crownbay:/sys/kernel/debug/tracing# echo 0 > /sys/block/sdc/trace/enable
|
|
|
+ </literallayout>
|
|
|
+ </para>
|
|
|
+ </section>
|
|
|
+ </section>
|
|
|
|
|
|
+ <section id='blktrace-documentation'>
|
|
|
+ <title>Documentation</title>
|
|
|
+
|
|
|
+ <para>
|
|
|
+ Online versions of the man pages for the commands discussed
|
|
|
+ in this section can be found here:
|
|
|
+ <itemizedlist>
|
|
|
+ <listitem><para><ulink url='http://linux.die.net/man/8/blktrace'>http://linux.die.net/man/8/blktrace</ulink>
|
|
|
+ </para></listitem>
|
|
|
+ <listitem><para><ulink url='http://linux.die.net/man/1/blkparse'>http://linux.die.net/man/1/blkparse</ulink>
|
|
|
+ </para></listitem>
|
|
|
+ <listitem><para><ulink url='http://linux.die.net/man/8/btrace'>http://linux.die.net/man/8/btrace</ulink>
|
|
|
+ </para></listitem>
|
|
|
+ </itemizedlist>
|
|
|
+ </para>
|
|
|
+
|
|
|
+ <para>
|
|
|
+ The above manpages, along with manpages for the other
|
|
|
+ blktrace utilities (btt, blkiomon, etc) can be found in the
|
|
|
+ /doc directory of the blktrace tools git repo:
|
|
|
+ <literallayout class='monospaced'>
|
|
|
+ $ git clone git://git.kernel.dk/blktrace.git
|
|
|
+ </literallayout>
|
|
|
+ </para>
|
|
|
+ </section>
|
|
|
</section>
|
|
|
</chapter>
|
|
|
<!--
|
Scott Rifenbark