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

[Aneesh Kumar K.V]

Michael Ellerman <mpe at 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
12408 records/s -> With patch with tracepoint enabled.

perf stat gave the below data for the above run.

 22,38,284      page-faults                                                 
 22,38,291      powerpc:hash_fault

I also used random_access_bench that Anton wrote, it actually
create lots of hash fault. A simple run gives.
(random_access_bench -o load -g -i -t 10 16G)

1,888      page-faults                                                 
2,64,283   powerpc:hash_fault                                          

random_access_bench gave:
1435.979 MB/s -> Without patch
1435.29  MB/s -> With patch with tracepoint disabled
1434.75  MB/s -> With patch with tracepoint enabled.

-aneesh