linux-kernel - Re: [PATCH 4/7] perf: be less pessimistic when scheduling events

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Message-ID: <20140211174804.GC12476@e106331-lin.cambridge.arm.com>
Date:	Tue, 11 Feb 2014 17:48:05 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	Dave P Martin <Dave.Martin@....com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 4/7] perf: be less pessimistic when scheduling events

On Mon, Feb 10, 2014 at 05:58:54PM +0000, Peter Zijlstra wrote:
> On Mon, Feb 10, 2014 at 05:44:21PM +0000, Mark Rutland wrote:
> > This patch makes ctx_flexible_sched_in attempt to schedule every group
> > in the flexible_groups list even when earlier groups failed to schedule,
> > enabling more groups to be scheduled simultaneously.
> 
> Since you're basically free to create as many events as you want, you can
> (as an unprivilidged user) make the context switch to and from your task
> arbitrarily expensive.

Not that it makes the approach any better, but surely this is already
the case for software events? I can create as many as I want, and
they'll always try to schedule.

I'll take a look into other ways to stop disparate PMUs' events from
adversely affecting each other. I guess it might not be possible to
solve the general problem without allowing said expensive context
switch.

Thanks,
Mark.
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