Re: [PATCH] events: Ensure that timers are updated without requiringread() call
From: Eric B Munson
Date: Thu Jun 23 2011 - 10:39:01 EST
On Thu, 23 Jun 2011, Peter Zijlstra wrote:
> On Thu, 2011-06-23 at 10:15 -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@xxxxxxxxx>
> > ---
> > kernel/events/core.c | 1 +
> > 1 files changed, 1 insertions(+), 0 deletions(-)
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 9efe710..3dd4ebe 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -3369,6 +3369,7 @@ void perf_event_update_userpage(struct perf_event *event)
> > struct perf_buffer *buffer;
> > rcu_read_lock();
> > + update_event_times(event);
> > buffer = rcu_dereference(event->buffer);
> > if (!buffer)
> > goto unlock;
> Not that easy, perf_event_update_userpage() can happen from NMI context,
> and update_event_times() needs to be done under ctx->lock.
I was afraid that might be the case, is there an easy-ish way to accomplish
the timer update?
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