Re: [PATCH 3/3] events: Ensure that timers are updated without requiring read() call

Eric B Munson
2011-06-24T12:44:25Z

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On Fri, 24 Jun 2011, Peter Zijlstra wrote:

> On Thu, 2011-06-23 at 16:34 -0400, Eric B Munson wrote:
> > The event tracing infrastructure exposes two timers which should be updated
> > each time the value of the counter is updated. Currently, these counters are
> > only updated when userspace calls read() on the fd associated with an event.
> > This means that counters which are read via the mmap'd page exclusively never
> > have their timers updated. This patch adds ensures that the timers are updated
> > each time the values in the mmap'd page are updated.
> >
> > Signed-off-by: Eric B Munson <emunson@mgebm.net>
> > ---
> > kernel/events/core.c | 12 ++++++++++++
> > 1 files changed, 12 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 9e9a7fa..e3be175 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -3382,6 +3382,18 @@ void perf_event_update_userpage(struct perf_event *event)
> > struct perf_buffer *buffer;
> >
> > rcu_read_lock();
> > + /*
> > + * compute total_time_enabled, total_time_running
> > + * based on snapshot values taken when the event
> > + * was last scheduled in.
> > + *
> > + * we cannot simply called update_context_time()
> > + * because of locking issue as we are called in
>
> s/are/can be/
>
> > + * NMI context
> > + */
> > + calc_timer_values(event,
> > + &event->total_time_enabled,
> > + &event->total_time_running);
>
> I'm not sure writing those from NMI context is a sane thing to do, best
> is to compute the values into a local variable and use that variable
> below.
>
> Took the first two patches.
>

Thanks, I will send out an updated patch once I get it tested.

Eric

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