linux-kernel - Re: [PATCH v4 0/2]: perf: reduce data loss when profiling highly parallel CPU bound workloads

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Date:   Wed, 29 Aug 2018 13:50:16 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/2]: perf: reduce data loss when profiling highly
 parallel CPU bound workloads

Hi,

On 29.08.2018 11:40, Alexey Budankov wrote:
> 
> Hi Kim,
> 
> On 28.08.2018 22:43, Kim Phillips wrote:
>> On Tue, 28 Aug 2018 18:44:57 +0300
>> Alexey Budankov <alexey.budankov@...ux.intel.com> wrote:
>>
>>> Experiment with profiling matrix multiplication code executing 128 
>>> threads on Intel Xeon Phi (KNM) with 272 cores, like below,
>>> demonstrates data loss metrics value of 98%:
>>
>> So I took these two patches for a quick test-drive on intel-pt.
> 
> Thanks for testing that out in this scenario! It hasn't been tested yet.
> 
>>
>> BEFORE (acme's today's perf/core branch):
>>
>> $ sudo perf version
>> perf version 4.18.rc7.g55fc647
>> $ sudo perf record -e intel_pt//  dd if=/dev/zero of=/dev/null count=100000
>> 100000+0 records in
>> 100000+0 records out
>> 51200000 bytes (51 MB, 49 MiB) copied, 0.0868081 s, 590 MB/s
>> [ perf record: Woken up 21 times to write data ]
>> [ perf record: Captured and wrote 41.302 MB perf.data ]
>> $ 
>>
>> AFTER (== BEFORE + these two patches):
>>
>> $ sudo ./perf version
>> perf version 4.18.rc7.gbc1c99
>> $ sudo perf record -e intel_pt//  dd if=/dev/zero of=/dev/null count=100000
>> 100000+0 records in
>> 100000+0 records out
>> 51200000 bytes (51 MB, 49 MiB) copied, 0.0931142 s, 550 MB/s
>>
>> ...and it's still running, minutes afterwards.  Before I kill it,
>> here's some strace output:
>>
>> nanosleep({tv_sec=0, tv_nsec=500000}, NULL) = 0
>> lseek(3, 332556518, SEEK_SET)           = 332556518
>> write(3, "D\0\0\0\0\0\10\0", 8)         = 8
>> lseek(3, 0, SEEK_CUR)                   = 332556526
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> nanosleep({tv_sec=0, tv_nsec=500000}, NULL) = 0
>> lseek(3, 332578462, SEEK_SET)           = 332578462
>> write(3, "D\0\0\0\0\0\10\0", 8)         = 8
>> lseek(3, 0, SEEK_CUR)                   = 332578470
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> nanosleep({tv_sec=0, tv_nsec=500000}, NULL) = 0
>> lseek(3, 332598822, SEEK_SET)           = 332598822
>> write(3, "D\0\0\0\0\0\10\0", 8)         = 8
>> lseek(3, 0, SEEK_CUR)                   = 332598830
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252c8, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e725200, FUTEX_WAKE_PRIVATE, 1) = 1
>> futex(0x7f221e7252cc, FUTEX_WAKE_PRIVATE, 1) = 1
>> ^Cstrace: Process 3597 detached
>>
>> I can't prove that it's these two patches that create the hang, but
>> this does look like a livelock situation...hm, hitting ^C doesn't stop
>> it...had to kill -9 it...erm, does 'perf record -e intel_pt// dd...'
>> work for you on a more standard machine?:
>>
>> $ dmesg | grep Perf
>> [    0.044226] Performance Events: PEBS fmt3+, Skylake events, 32-deep LBR, full-width counters, Intel PMU driver.
> 
> Strace patterns look similar to the ones implemented in the patches. 
> Let me reproduce and investigate the hang locally.

The stack:

Thread 1 (Thread 0x7f170ef4a7c0 (LWP 11182)):
#0  0x00007f170e2dc350 in nanosleep () from /lib64/libpthread.so.0
#1  0x00000000004436e4 in record__mmap_read_sync (trace_fd=3, cblocks=0x275c120, cblocks_size=6, rec=0xabe1c0 <record>) at builtin-record.c:561
#2  0x0000000000443c71 in record__mmap_read_evlist (rec=0xabe1c0 <record>, evlist=0x274f4f0, overwrite=false) at builtin-record.c:671
#3  0x0000000000443d21 in record__mmap_read_all (rec=0xabe1c0 <record>) at builtin-record.c:692
#4  0x0000000000444feb in __cmd_record (rec=0xabe1c0 <record>, argc=4, argv=0x7fffda7606f0) at builtin-record.c:1183
#5  0x00000000004464dc in cmd_record (argc=4, argv=0x7fffda7606f0) at builtin-record.c:2000
#6  0x00000000004cee9e in run_builtin (p=0xace5f8 <commands+216>, argc=8, argv=0x7fffda7606f0) at perf.c:302
#7  0x00000000004cf10b in handle_internal_command (argc=8, argv=0x7fffda7606f0) at perf.c:354
#8  0x00000000004cf25a in run_argv (argcp=0x7fffda76054c, argv=0x7fffda760540) at perf.c:398
#9  0x00000000004cf5c6 in main (argc=8, argv=0x7fffda7606f0) at perf.c:520

The main thread continue consuming kernel buffers even 
after the application finishes:

Using CPUID GenuineIntel-6-5E
mmap size 528384B
sync: sched: cblock 0x7fd1d62f0088 size 192
sync: sched: cblock 0x7fd1d63102c8 size 192
sync: sched: cblock 0x7fd1d63203e8 size 288
sync: sched: cblock 0x7fd1d6360868 size 1024
sync: done: cblock 0x7fd1d62f0088
sync: done: cblock 0x7fd1d63102c8
sync: done: cblock 0x7fd1d63203e8
sync: done: cblock 0x7fd1d6360868
...
sync: done: cblock 0x7fd1d62f0088
sync: done: cblock 0x7fd1d63102c8
sync: sched: cblock 0x7fd1d62f0088 size 192
sync: sched: cblock 0x7fd1d63102c8 size 192
sync: done: cblock 0x7fd1d62f0088
sync: done: cblock 0x7fd1d63102c8
sync: sched: cblock 0x7fd1d62f0088 size 192
sync: sched: cblock 0x7fd1d63102c8 size 192
sync: done: cblock 0x7fd1d62f0088
sync: done: cblock 0x7fd1d63102c8
sync: sched: cblock 0x7fd1d62f0088 size 192
sync: sched: cblock 0x7fd1d63102c8 size 192
sync: sched: cblock 0x7fd1d6360868 size 128
100000+0 records in
100000+0 records out
51200000 bytes (51 MB, 49 MiB) copied, 0.0622905 s, 822 MB/s
sig: 17
sync: done: cblock 0x7fd1d62f0088
sync: done: cblock 0x7fd1d63102c8
sync: sched: cblock 0x7fd1d62f0088 size 192
sync: sched: cblock 0x7fd1d63001a8 size 192
sync: sched: cblock 0x7fd1d63102c8 size 192
sync: sched: cblock 0x7fd1d6360868 size 416
sync: done: cblock 0x7fd1d62f0088
sync: done: cblock 0x7fd1d63001a8
sync: done: cblock 0x7fd1d63102c8
sync: done: cblock 0x7fd1d6360868
sync: sched: cblock 0x7fd1d62f0088 size 192
sync: sched: cblock 0x7fd1d63001a8 size 192
sync: sched: cblock 0x7fd1d63102c8 size 192
...

> 
> Thanks,
> Alexey
> 
>>
>> Thanks,
>>
>> Kim
>>
>