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

Avi Kivity
2011-07-12T07:20:27Z

On 07/12/2011 12:07 AM, Will Deacon wrote:
> On Mon, Jul 04, 2011 at 03:36:57PM +0100, Frederic Weisbecker wrote:
> > On Mon, Jul 04, 2011 at 05:10:20PM +0300, Avi Kivity wrote:
> > > On 07/04/2011 04:58 PM, Frederic Weisbecker wrote:
> > > >Another thing I would like to do in the even longer term is to not use perf anymore
> > > >for ptrace breakpoints, because that involves a heavy dependency and few people are
> > > >happy with that. Instead we should just have a generic hook into the sched_switch()
> > > >and handle pure ptrace breakpoints there. The central breakpoint API would still be
> > > >there to reserve/schedule breakpoint resources between ptrace and perf.
> > > >
> > >
> > > 'struct preempt_notifier' may be the hook you're looking for.
> >
> > Yeah looks like a perfect fit as it's per task.
>
> I had a quick look at this and I think the preempt_notifier stuff needs
> slightly extending so that we can register a notifier for a task other than
> current [e.g. the child of current on which we are installing breakpoints].
>
> If the task in question is running, it looks like this will introduce a race
> condition between notifier registration and rescheduling. For the purposes
> of ptrace this shouldn't be a problem as the child will be stopped, but
> others might also want to make use of the new functionality.
>
> Any ideas on how this could be achieved, or am I better off just restricting
> this to children that are being traced?

Maybe we need a generic "run this function in this task's context"
mechanism instead. Like an IPI, but targeting tasks instead of cpus.

--
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