Re: [PATCH 1/3] perf: add context field to perf_event

Peter Zijlstra
2011-07-12T09:55:19Z

On Tue, 2011-07-12 at 12:16 +0300, Avi Kivity wrote:
> On 07/12/2011 12:14 PM, Peter Zijlstra wrote:
> > On Tue, 2011-07-12 at 12:08 +0300, Avi Kivity wrote:
> > > Similar, but with stronger guarantees: when the function is called,
> > > current == p, and the task was either sleeping or in userspace.
> >
> > If the task is sleeping, current can never be p.
>
> The guarantee is that the task was sleeping just before the function is
> called. Of course it's woken up to run the function.
>
> The idea is that you run the function in a known safe point to avoid
> extra synchronization.
>

I'd much rather we didn't wake the task and let it sleep, that's usually
a very safe place for tasks to be. All you'd need is a guarantee it
won't be woken up while you're doing your thing.