linux-kernel - Re: [PATCH 2/4] perf/ftrace: Fix function trace events

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Date:   Wed, 11 Oct 2017 18:40:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     zhouchengming <zhouchengming1@...wei.com>
Cc:     rostedt@...dmis.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, jolsa@...nel.org
Subject: Re: [PATCH 2/4] perf/ftrace: Fix function trace events

On Wed, Oct 11, 2017 at 05:02:28PM +0800, zhouchengming wrote:
> On 2017/10/11 15:45, Peter Zijlstra wrote:

> > +		if (!(flags&  PERF_EF_START))
> > +			p_event->hw.state = PERF_HES_STOPPED;
> 
> Don't we need to check the flags for ftrace perf_event?
> So if we should put this outside the if (!tp_event->class->reg()) ?

Oh, right you are, that's independent of the hlist nonsense.

> > +		list = this_cpu_ptr(pcpu_list);
> > +		hlist_add_head_rcu(&p_event->hlist_entry, list);
> > +	}
> 
> Now we don't add perf_event to the pcpu_list, so we also can avoid
> to alloc pcpu_list for function tp_event in perf_trace_event_reg().

Yeah that allocation is superfluous, Not entirely sure how to cleanly
get rid of that though; that's another web to untangle.