Michael Ellerman <m...@ellerman.id.au> writes:
> On Wed, 2015-01-21 at 14:15 +0530, Aneesh Kumar K.V wrote:
>> Michael Ellerman <m...@ellerman.id.au> writes:
>>
>> > On Tue, 2015-01-20 at 17:05 +0530, Aneesh Kumar K.V wrote:
>> >> This enables us to understand how many hash fault we are taking
>> >> when running benchmarks.
>> >>
>> >> For ex:
>> >> -bash-4.2# ./perf stat -e powerpc:hash_fault -e page-faults
>> >> /tmp/ebizzy.ppc64 -S 30 -P -n 1000
>> >> ...
>> >>
>> >> Performance counter stats for '/tmp/ebizzy.ppc64 -S 30 -P -n 1000':
>> >>
>> >> 1,10,04,075 powerpc:hash_fault
>> >> 1,10,03,429 page-faults
>> >>
>> >> 30.865978991 seconds time elapsed
>> >
>> > Looks good.
>> >
>> > Can you attach some test results that show it's not hurting performance
>> > when
>> > it's disabled.
>>
>> ebizzy with -S 30 -t 1 -P gave
>> 13627 records/s -> Without patch
>> 13546 records/s -> With patch with tracepoint disabled
>
> OK. So that's about -0.6%. Are we happy with that? I'm not sure.
>
> Can you do a few more runs and see if that's a stable result.
That is within the run variance for that test. Infact I found it
difficult to get a stable records/s with ebizzy run, even after fixing
the random state variable and forcing single thread. I ended up doing
a micro benchmark that allocate a large region and touch one byte per
page.
That resulted in
time perf stat -e page-faults -e powerpc:hash_fault ./a.out
Performance counter stats for './a.out':
10,00,062 page-faults
10,00,068 powerpc:hash_fault
12.414350121 seconds time elapsed
real 0m12.558s
user 0m0.577s
sys 0m11.932s
and with that test we have an average system time for 10 run
Without patch
sys: 0m11.2425
With patch:
sys: 0m11.3258
ie, a -0.7% impact
If that impact is high we could possibly put that tracepoint within #ifdef
CONFIG_DEBUG_VM ?
-aneesh
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