linux-kernel - Re: [PATCH 03/12] perf: add perf_event_task

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Date:	Wed, 05 May 2010 07:16:31 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	mingo@...e.hu, peterz@...radead.org, efault@....de, avi@...hat.com,
	paulus@...ba.org, acme@...hat.com, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 03/12] perf: add perf_event_task_migrate()

Hello,

On 05/05/2010 07:08 AM, Frederic Weisbecker wrote:
>>  /*
>> + * Called from scheduler set_task_cpu() to notify migration events.
>> + * If the task is moving to a different cpu, generate a migration sw
>> + * event.
>> + */
>> +void perf_event_task_migrate(struct task_struct *task, int new_cpu)
>> +{
>> +	if (task_cpu(task) != new_cpu)
>> +		perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 1, NULL, 0);
>> +}
> 
> This needs to be static and inline (I haven't seem external users in this
> patchset).

Hmm... after the last patch, this one becomes a TP probe function
which can't be inlined.

> And we want it to be inlined because we save the caller address and the frame
> pointer from perf_sw_event(), and a new level of call is not wanted here.

Oh I see.  So, to use it with TP, I would need increase the @skip
parameter to perf_fetch_caller_regs() somehow, right?  Also, it
probably would be a good idea to add a comment w/ big fat warning to
perf_sw_event().

>> @@ -2084,11 +2084,10 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
>>  #endif
>>  
>>  	trace_sched_migrate_task(p, new_cpu);
>> +	perf_event_task_migrate(p, new_cpu);
>>  
>> -	if (task_cpu(p) != new_cpu) {
>> +	if (task_cpu(p) != new_cpu)
> 
> In fact why not moving both tracing calls under this check.
> This is going to fix the migrate trace event that gets called
> even on "spurious" migrations, and you avoid the duplicate check
> in the perf callback.

Yeah, that would be my preferred choice too.  I just didn't know that
could be changed.  Cool.  I'll.

Thanks.

-- 
tejun
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