Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events

[David Ahern <dsahern@gmail.com>]

On 3/27/15 7:10 AM, Don Zickus wrote:
> I talked with Joe on my way out the door yesterday and he confirmed, just
> removing -BN from our test showed a performance hit with your patch.  With
> the -BN option, there is no performance hit and we are perfectly fine with
> your patch.
>
> So, I guess I am confused how the -BN and your patch could change behaviour.

I am too. This change has nothing to do with buildid's and scanning the 
buildid code setting the ppid correctly should not cause any extra work.

Arnaldo: any thoughts?

>
> Just to re-iterate what we did, Joe kicked off a specJBB run and he did 20
> captures of two runs (one with the unpatched binary and one with a pached
> binary).
>
> for i in {1..20}
> do
>    time perf.unpatched mem record -a -e cpu/mem-loads,ldlat=50/pp -e cpu/mem-stores/pp sleep 10
>    time perf.patched   mem record -a -e cpu/mem-loads,ldlat=50/pp -e cpu/mem-stores/pp sleep 10
> done
>
> then we repeat the above test but with -BN in both runs.  We compare the
> log sizes to make sure they are similar for the random snapshots and compare
> the times.  With the -BN option, the times are generally within +/- 0.5
> seconds of each.  Without the -BN option the patched perf binary is
> generally +20-40 seconds slower.
>
>
>
> However, based on your description above about what the -BN option does, I
> am scratching my head about our results.  Thoughts?

Try this:
perf record -o unpatched.data -g -- perf.unpatched mem record -a -e 
cpu/mem-loads,ldlat=50/pp -e cpu/mem-stores/pp sleep 10

perf record -o patched.data -g -- perf.patched mem record -a -e 
cpu/mem-loads,ldlat=50/pp -e cpu/mem-stores/pp sleep 10

And then compare the reports for each.

David