linux-kernel - Re: [PATCH] perf_events: improve x86 event scheduling (v5)

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Message-ID: <1263822898.4283.558.camel@laptop>
Date:	Mon, 18 Jan 2010 14:54:58 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, perfmon2-devel@...ts.sf.net, eranian@...il.com
Subject: Re: [PATCH]  perf_events: improve x86 event scheduling (v5)

On Mon, 2010-01-18 at 14:43 +0100, Frederic Weisbecker wrote:
> 
> Shouldn't we actually use the core based pmu->enable(),disable()
> model called from kernel/perf_event.c:event_sched_in(),
> like every other events, where we can fill up the queue of hardware
> events to be scheduled, and then call a hw_check_constraints()
> when we finish a group scheduling? 

Well the thing that makes hw_perf_group_sched_in() useful is that you
can add a bunch of events and not have to reschedule for each one, but
instead do a single schedule pass.

That said you do have a point, maybe we can express this particular
thing differently.. maybe a pre and post group call like:

 void hw_perf_group_sched_in_begin(struct pmu *pmu)
 int  hw_perf_group_sched_in_end(struct pmu *pmu)

That way we know we need to track more state for rollback and can give
the pmu implementation leeway to delay scheduling/availablility tests.

Paul, would that work for you too?

Then there's still the question of having events of multiple hw pmus in
a single group, I'd be perfectly fine with saying that's not allowed,
what to others think?

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