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SubjectRe: [LKP] [lkp] [perf powerpc] 18d1796d0b: [No primary change]
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Peter Zijlstra <peterz@infradead.org> writes:

> On Tue, Oct 25, 2016 at 02:40:13PM +0800, kernel test robot wrote:
>> [will-it-scale] perf-stat.branch-miss-rate +7.4% regression
>> Reply-To: kernel test robot <xiaolong.ye@intel.com>
>> User-Agent: Heirloom mailx 12.5 6/20/10
>>
>>
>> FYI, we noticed a +7.4% regression of perf-stat.branch-miss-rate due to commit:
>>
>> commit 18d1796d0b45762ec6f58c5ed2ad3f7510ffbaa9 ("perf powerpc: Don't call perf_event_disable from atomic context")
>> https://github.com/0day-ci/linux Jiri-Olsa/perf-powerpc-Don-t-call-perf_event_disable-from-atomic-context/20161006-203500
>>
>> in testcase: will-it-scale
>> on test machine: 32 threads Intel(R) Xeon(R) CPU E5-2680 0 @ 2.70GHz with 64G memory
>> with following parameters:
>>
>> test: poll2
>> cpufreq_governor: performance
>>
>> Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
>
>> Details are as below:
>> -------------------------------------------------------------------------------------------------->
>>
>>
>> To reproduce:
>>
>> git clone git://git.kernel.org/pub/scm/linux/kernel/git/wfg/lkp-tests.git
>> cd lkp-tests
>> bin/lkp install job.yaml # job file is attached in this email
>> bin/lkp run job.yaml
>>
>> =========================================================================================
>> compiler/cpufreq_governor/kconfig/rootfs/tbox_group/test/testcase:
>> gcc-6/performance/x86_64-rhel-7.2/debian-x86_64-2016-08-31.cgz/lkp-sb03/poll2/will-it-scale
>>
>> commit:
>> 41aad2a6d4 (" perf/core improvements and fixes:")
>> 18d1796d0b ("perf powerpc: Don't call perf_event_disable from atomic context")
>>
>> 41aad2a6d4fcdda8 18d1796d0b45762ec6f58c5ed2
>> ---------------- --------------------------
>> fail:runs %reproduction fail:runs
>> | | |
>> %stddev %change %stddev
>> \ | \
>> 0.19 . 0% +7.4% 0.21 . 0% perf-stat.branch-miss-rate%
>> 9.591e+09 . 1% +9.1% 1.047e+10 . 0% perf-stat.branch-misses
>> 1.962e+09 . 0% +2.3% 2.008e+09 . 1% perf-stat.cache-references
>> 51.18 . 2% +5.6% 54.06 . 1% perf-stat.iTLB-load-miss-rate%
>> 46430577 . 5% -6.9% 43241506 . 2% perf-stat.iTLB-loads
>> 9.90 . 4% +9.3% 10.82 . 4% turbostat.Pkg%pc2
>> 62066 . 24% +34.7% 83582 . 11% numa-meminfo.node1.Active
>> 49531 . 30% +42.9% 70778 . 13% numa-meminfo.node1.Active(anon)
>> 27883 .100% -100.0% 0.00 . -1% latency_stats.avg.proc_cgroup_show.proc_single_show.seq_read.__vfs_read.vfs_read.SyS_read.do_syscall_64.return_from_SYSCALL_64
>> 27883 .100% -100.0% 0.00 . -1% latency_stats.max.proc_cgroup_show.proc_single_show.seq_read.__vfs_read.vfs_read.SyS_read.do_syscall_64.return_from_SYSCALL_64
>> 32685 . 38% +88.5% 61603 .147% latency_stats.sum.call_rwsem_down_write_failed.path_openat.do_filp_open.do_sys_open.SyS_open.entry_SYSCALL_64_fastpath
>> 27883 .100% -100.0% 0.00 . -1% latency_stats.sum.proc_cgroup_show.proc_single_show.seq_read.__vfs_read.vfs_read.SyS_read.do_syscall_64.return_from_SYSCALL_64
>> 92795 . 4% -8.6% 84853 . 6% numa-vmstat.node0.numa_hit
>> 92782 . 4% -8.5% 84851 . 6% numa-vmstat.node0.numa_local
>> 12381 . 30% +42.9% 17694 . 13% numa-vmstat.node1.nr_active_anon
>> 12381 . 30% +42.9% 17694 . 13% numa-vmstat.node1.nr_zone_active_anon
>> 21.80 . 59% -69.8% 6.58 . 83% sched_debug.cpu.clock.stddev
>> 21.80 . 59% -69.8% 6.58 . 83% sched_debug.cpu.clock_task.stddev
>> 0.00 . 23% -34.3% 0.00 . 20% sched_debug.cpu.next_balance.stddev
>> 35829 . 9% -18.4% 29221 . 6% sched_debug.cpu.nr_switches.max
>> 8361 . 6% -13.4% 7243 . 7% sched_debug.cpu.nr_switches.stddev
>> 8.43 . 11% -25.2% 6.30 . 12% sched_debug.cpu.nr_uninterruptible.stddev
>> 18057 . 6% -14.3% 15482 . 8% sched_debug.cpu.sched_count.stddev
>>
>
> ARGH... so what is the normal metric for this test and did that change?
> And why can't I still find that? These reports suck!

There is observable changes between the benchmark (will-it-scale)
scores. That is said in the subject of the mail: "[No primary
change]". But apparently, that is not clear. We will improve that to
make it more clear.

> The result doesn't make sense, my gcc inlines the function call, the
> emitted code is very similar to the old code, with exception of one
> extra symbol.
>
> Are you sure this isn't simple run to run variation?

The reported change is perf-stat.branch-miss-rate%, which is changed
from 0.19% to 0.21%. That is too small. So, please ignore this
report. We will be more careful in the future.

Best Regards,
Huang, Ying

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