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

[David Ahern]

On 3/25/15 1:15 PM, Don Zickus wrote:
> On Wed, Mar 25, 2015 at 10:51:10AM -0600, David Ahern wrote:
> > 363b785f38 added synthesized fork events and set a thread's parent id
> > to itself. Since we are already processing /proc/<pid>/status the ppid
> > can be determined properly. Make it so.
> >
> > Performance impact measured on a sparc based T5-8 (1024 CPUs):
> > $ ps -efL | wc -l
> > 20185
> >
> > Current code:
> > $ time perf record -o perf-no-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
> > mmap size 532480B
> > [ perf record: Woken up 0 times to write data ]
> > failed to write feature 9
> > [ perf record: Captured and wrote 0.000 MB perf-no-ppid.data ]
> >
> > real	0m26.144s
> > user	0m0.452s
> > sys	0m25.564s
> >
> > With PPID patch:
> > $ time ./perf_ppid record -o perf-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
> > mmap size 532480B
> > [ perf record: Woken up 0 times to write data ]
> > failed to write feature 9
> > [ perf record: Captured and wrote 0.000 MB perf-ppid.data ]
> >
> > real	0m25.743s
> > user	0m0.268s
> > sys	0m25.368s
> >
> > Signed-off-by: David Ahern <dsahern@xxxxxxxxx>
> > Cc: Don Zickus <dzickus@xxxxxxxxxx>
> > Cc: Joe Mario <jmario@xxxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > v2:
> > - removed loop in place of 1 read and processing a buffer
>
> Hmm, I am not entirely sure this is correct.  You made an optimization that
> hides the negative impact your patch does.  I would prefer you split this
> patch into two pieces.  One with the read loop optimization (which I think
> is great) and the second is your ppid change.
>
> I would then like to redo our test with the first patch applied and then
> both patches applied.

From your other response I take it you understand the patch now? It is 
a matter of semantics to break this single into 2 -- optimize the 
existing code and then add the ppid. End result will be what this patch 
shows. Before I do that can you /Joe confirm the performance is acceptable?

Thanks,

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