linux-kernel - Re: [PATCH v2 2/3] perf: use hrtimer for event multiplexing

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Message-ID: <CABPqkBQr-nfwEdw_k5fZKrVUjyPYpSr_KQPoOsUp7ykcL4-QmA@mail.gmail.com>
Date:	Thu, 13 Sep 2012 14:27:50 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Robert Richter <robert.richter@....com>
Subject: Re: [PATCH v2 2/3] perf: use hrtimer for event multiplexing

On Thu, Sep 13, 2012 at 2:26 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2012-09-13 at 14:20 +0200, Stephane Eranian wrote:
>> On Thu, Sep 13, 2012 at 2:16 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> > On Wed, 2012-09-12 at 17:37 +0200, Stephane Eranian wrote:
>> >
>> >> Note however that the rotation_list is still used in perf_event_task_tick()
>> >> to iterate over the ctx which needs unthrottling. We would have to switch
>> >> that loop over to a for-each-pmu() which would necessary incur more
>> >> iterations as it would include all the SW PMUs.
>> >
>> > Oh urgh, right. I think that was one of the reasons I bailed on the
>> > hrtimer thing, the frequency and throttle stuff.
>> >
>> > ctx->nr_freq and needs_unthr could help, but yeah.
>>
>> I think for now, we could keep rotation list for the unthrottling.
>> Multiplexing won't use rotation_list anymore.
>
> wouldn't that still have the problem where we take the sw-pmus off of
> the rotation-list?

No because we should not use the patch I posted last week. So rotation_start()
would still enqueue SW pmus.
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