Re: [RFC -v3 PATCH 2/3] sched: add yield_to function

Avi Kivity
2011-01-05T17:35:44Z

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?

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