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

Avi Kivity
2011-06-29T16:26:21Z

On 06/29/2011 07:08 PM, Frederic Weisbecker wrote:
> On Wed, Jun 29, 2011 at 06:42:35PM +0300, Avi Kivity wrote:
> > The perf_event overflow handler does not receive any caller-derived
> > argument, so many callers need to resort to looking up the perf_event
> > in their local data structure. This is ugly and doesn't scale if a
> > single callback services many perf_events.
> >
> > Fix by adding a context parameter to perf_event_create_kernel_counter()
> > (and derived hardware breakpoints APIs) and storing it in the perf_event.
> > The field can be accessed from the callback as event->overflow_handler_context.
> > All callers are updated.
> >
> > Signed-off-by: Avi Kivity<avi@redhat.com>
>
> I believe it can micro-optimize ptrace through register_user_hw_breakpoint() because
> we could store the index of the breakpoint that way, instead of iterating through 4 slots.
>

Right, I noticed that while writing the patch.

> Perhaps it can help in arm too, adding Will in Cc.
>
> But for register_wide_hw_breakpoint, I'm not sure. kgdb is the main user, may be Jason
> could find some use of it.

I think an API should not require its users to iterate in their
callbacks, even if it doesn't affect current users for some reason.

--
error compiling committee.c: too many arguments to function