Re: [PATCH 2/2] perf lock: New subcommand "lock" to perf for analyzing lock statistics

[Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>]

Hi Frederic,

Frederic Weisbecker wrote:

> This profile has been done using ftrace with perf right?

We not use perf, just operate it by debugfs, the test procedure
is like below:

case 1: disable all trace events:
echo nop > debugfs/tracing/current_tracer
echo > debugfs/tracing/set_event
run benchmarks
...

case 2: enable all trace events except lockdep:
echo nop > debugfs/tracing/current_tracer
echo *:* > debugfs/tracing/set_event
echo 0 >  debugfs/tracing/events/lockdep/enable
run benchmarks
...

> In one of your previous mails, you showed us the difference
> of the size of perf.data by capturing either scheduler events
> or lock events.
> 

It's not my work :-)

Thanks,
Xiao

> And IIRC, the case of lock events resulted in a 100 MB perf.data
> whereas it was a small file for sched events.
> 
> The overhead in the pagefault and mmap latency could then
> result in the fact we have much more events to save, walking
> through much more pages in perf buffer, then faulting more often,
> etc.
> 
> Plus the fact various locks are taken in mmap and fault path,
> generating more lock events.
> 
> Just a guess...
> 
> 
>