On Tue, 28 Aug 2018 18:44:57 +0300
Alexey Budankov <alexey.budan...@linux.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.
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.
Thanks,
Kim
