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

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Date:	Wed, 05 Jan 2011 18:28:31 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Avi Kivity <avi@...hat.com>
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 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.

>   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.
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