linux-kernel - Re: [RFC -v3 PATCH 2/3] sched: add yield

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Message-ID: <4D24ABD7.4040503@redhat.com>
Date:	Wed, 05 Jan 2011 19:35:19 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, Tejun Heo <tj@...nel.org>
CC:	Rik van Riel <riel@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function

On 01/05/2011 07:28 PM, Peter Zijlstra wrote:
> On Wed, 2011-01-05 at 19:19 +0200, Avi Kivity wrote:
> >  On 01/05/2011 07:15 PM, Peter Zijlstra wrote:
> >  >  On Wed, 2011-01-05 at 19:10 +0200, Avi Kivity wrote:
> >  >  >   On 01/04/2011 08:04 PM, Peter Zijlstra wrote:
> >  >  >   >   This definitely wants to be EXPORT_SYMBOL_GPL() and if it were possible
> >  >  >   >   I'd make it so only kvm.o could use it. It really sucks that kvm is a
> >  >  >   >   module.
> >  >  >
> >  >  >   Why does it suck?  I mean apart from the "virtualization is crap" song.
> >  >
> >  >  Because it needs hooks all over the core kernel, like this yield_to()
> >  >  stuff. Exporting this might lead to others wanting to use it too.
> >
> >  Well, it's very convenient for development (modprobe vs. reboot).
>
> Get a machine that boots fast ;-), it might be because I've never worked
> on anything modular, but typically stuff crashes when I got it wrong, in
> which case you're forced to power-cycle anyway.

I often get by with just guest crashes.  Or maybe it oopses, I look 
around, then reboot at my leisure.

> >    What hooks do you object to?
>
> Don't really keep a list, but every now and again see something that
> makes me think that ought not be exported.
>
> >  mmu notifiers are useful for some drivers, sched
> >  notifiers are useful for cmwq and possibly perf?
>
> Both use explicit function calls because its easier to read the code and
> faster.

I doubt it's measurable, especially for perf with the msr tweaking it does.

Tejun, why did you end up not using preempt_notifiers in cmwq?

-- 
error compiling committee.c: too many arguments to function

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