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Date: Thu, 10 Jun 2010 18:12:37 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Paul Mackerras <paulus@samba.org>,
       Stephane Eranian <eranian@google.com>,
       Cyrill Gorcunov <gorcunov@gmail.com>,
       Zhang Yanmin <yanmin_zhang@linux.intel.com>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 1/5] perf: Provide a proper stop action for software
	events
Message-ID: <20100610161234.GA5255@nowhere>
References: <1276141760-11590-1-git-send-regression-fweisbec@gmail.com> <1276141760-11590-2-git-send-regression-fweisbec@gmail.com> <1276166813.2077.96.camel@twins> <1276168242.2077.134.camel@twins>
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On Thu, Jun 10, 2010 at 01:10:42PM +0200, Peter Zijlstra wrote:
> On Thu, 2010-06-10 at 12:46 +0200, Peter Zijlstra wrote:
> > 
> > Something like the below would work, the only 'problem' is that it grows
> > hw_perf_event.
> 
> If we do the whole PAUSEd thing right, we'd not need this I think.


It's not needed, and moreover software_pmu:stop/start() can be the same
than software:pmu:disable/enable() without the need to add another check
in the fast path.

But we need perf_event_stop/start() to work on software events. And in fact
now that we use the hlist_del_init, it's safe, but a bit wasteful in
the period reset path. That's another problem that is not critical, but
if you want to solve this by ripping the differences between software and
hardware (which I agree with), we need a ->reset_period callback.