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

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Date:	Tue, 19 Jan 2010 16:55:11 +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 Tue, Jan 19, 2010 at 02:24:49PM +0100, Peter Zijlstra wrote:
> Hrmph, so I read some of that hw_breakpoint stuff, and now I'm sorta
> confused, it looks like ->enable should never fail, but that means you
> cannot overcommit breakpoints, which doesn't fit the perf model nicely.



Yeah :)
I described this in my previous mail to you. Breakpoint events, for
now, are not supposed to fail on enable().


But once we have the strict pinned -> flexible ordering,
I'll rework this.

 
> Also, I see you set an ->unthrottle, but then don't implement it, but
> comment it as todo, which is strange because that implies its broken. If
> there's an ->unthrottle method it will throttle, so if its todo, the
> safest thing is to not set it.


Yeah, that's because I have a too vague idea on what is the purpose
of the unthrottle() callback.

I've read the concerned codes that call this, several times, and I still
can't figure out what happens there, not sure what is meant by throttle
or unthrottle there :-/

 
> /me mutters something and goes look at something else for a while.


Yeah, that's still a young code that needs improvement :)

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