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

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Message-ID: <20100118161836.GG10364@nowhere>
Date:	Mon, 18 Jan 2010 17:18:38 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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, Jan 18, 2010 at 03:56:41PM +0100, Peter Zijlstra wrote:
> On Mon, 2010-01-18 at 15:45 +0100, Frederic Weisbecker wrote:
> > 
> > > > That requires to know in advance if we have hardware pmu
> > > > in the list though (can be a flag in the group).
> > > 
> > > Good point, but your proposed hw_check_constraint() call needs to know
> > > the exact same.
> > 
> > 
> > True. Whatever model we use anyway, both implement the same idea.
> 
> Hmm, we seem to already have that problem (which would indicate another
> bug in the hw-breakpoint stuff), how do you deal with
> hw_perf_{enable,disable}() for the breakpoints?


We don't have ordering constraints for breakpoints, only constraints
on the number of available registers.

So we check the constraints when a breakpoint registers. The
enable/disable then (is supposed to) always succeed on breakpoint
pmu, except for flexible breakpoints that can make it or not,
but no need to overwrite group scheduling for that.

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