Subject: Re: [PATCH] powerpc/mm: Add trace point for tracking hash pte fault

From: Michael Ellerman <[email-masked]>
Date: Wed, 28 Jan 2015 17:11:07 +1100

On Wed, 2015-01-21 at 14:15 +0530, Aneesh Kumar K.V wrote:
> Michael Ellerman <[email-masked]> 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.

> random_access_bench gave:
> 1435.979 MB/s -> Without patch
> 1435.29  MB/s -> With patch with tracepoint disabled

That's more like -0.05% which is in the noise.

cheers