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Date: Tue, 22 Jun 2010 18:26:55 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: paulus <paulus@samba.org>, stephane eranian <eranian@googlemail.com>,
       Robert Richter <robert.richter@amd.com>,
       Will Deacon <will.deacon@arm.com>, Paul Mundt <lethal@linux-sh.org>,
       Cyrill Gorcunov <gorcunov@gmail.com>, Lin Ming <ming.m.lin@intel.com>,
       Yanmin <yanmin_zhang@linux.intel.com>,
       Deng-Cheng Zhu <dengcheng.zhu@gmail.com>,
       David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 8/8] perf: Rework the PMU methods
Message-ID: <20100622162652.GB5458@nowhere>
References: <20100616160027.590430763@chello.nl> <20100616160238.721536975@chello.nl> <20100618042143.GE5345@nowhere> <1276845338.27822.1450.camel@twins>
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On Fri, Jun 18, 2010 at 09:15:38AM +0200, Peter Zijlstra wrote:
> On Fri, 2010-06-18 at 06:21 +0200, Frederic Weisbecker wrote:
> > On Wed, Jun 16, 2010 at 06:00:35PM +0200, Peter Zijlstra wrote:
> > > -static void x86_pmu_stop(struct perf_event *event)
> > > +static void x86_pmu_stop(struct perf_event *event, int flags)
> > >  {
> > > -	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> > > -	struct hw_perf_event *hwc = &event->hw;
> > > -	int idx = hwc->idx;
> > > -
> > >  	if (!__test_and_clear_bit(idx, cpuc->active_mask))
> > > -		return;
> > 
> > 
> > 
> > Do you still need active_mask now that you have HES_STOPPED?
> 
> there still were some users, but yeah, we cuold probably clean that up,
> bit since the patch is large enough as is, I didn't attempt that.


Yeah, that can be done later.


 
> > > +static void perf_swevent_start(struct perf_event *event, int flags)
> > > +{
> > > +	event->hw.state = 0;
> > > +}
> > > +
> > > +static void perf_swevent_stop(struct perf_event *event, int flags)
> > >  {
> > > +	event->hw.state = 1;
> > >  }
> > 
> > 
> > So, instead of doing this and add yet another check in the fast path,
> > what about just playing with the hlist insertion and deletion?
> 
> I wanted to avoid too much trickery, first make a simple one work, then
> try something fancy.



Ok, as far it's not considered a long term thing. I can
improve that from my exclusion patchset, rebased on top of yours.




> > It would be nice to have a PERF_EF_STOP as well in ->del, so that
> > each pmu don't need to maintain an internal state.
> 
> You have to track it since we can stop the thing outselves without the
> caller knowing.


>>From the pmu internals yeah, that's what the x86 pmu does. But otherwise, other
pmu don't do such things.