linux-kernel - Re: [PATCH 1/2] kvm: use modern cpumask primitives, no cpumask

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Message-Id: <200812081638.07526.rusty@rustcorp.com.au>
Date:	Mon, 8 Dec 2008 16:38:07 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Avi Kivity <avi@...hat.com>
Cc:	"kvm-devel" <kvm@...r.kernel.org>, linux-kernel@...r.kernel.org,
	Mike Travis <travis@....com>
Subject: Re: [PATCH 1/2] kvm: use modern cpumask primitives, no cpumask_t on stack

On Monday 08 December 2008 02:44:00 Avi Kivity wrote:
> Avi Kivity wrote:
> > Rusty Russell wrote:
> >> We're getting rid on on-stack cpumasks for large NR_CPUS.
> >>
> >> 1) Use cpumask_var_t and alloc_cpumask_var (a noop normally).  Fallback
> >>    code is inefficient but never happens in practice.
> >
> > Wow, code duplication from Rusty. Things must be bad.
> >
> > Since we're in a get_cpu() here, how about a per_cpu static cpumask 
> > instead? I don't mind the inefficient fallback, just the duplication.
> >
> 
> Btw, for the general case, instead of forcing everyone to duplicate, how 
> about:
> 
> cpumask_var_t cpus;
> 
> with_cpumask(cpus) {
>    ... code to populate cpus
>    smp_call_function_some(...);
> } end_with_cpumask(cpus);
> 
> Where with_cpumask() allocates cpus, and uses a mutex + static fallback 
> on failure.

I'd prefer not to hide deadlocks that way :(

I'll re-battle with that code to neaten it.  There are only a few places
which have these kind of issues.

Thanks,
Rusty.
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