Messages in this thread | | | Subject | Re: [PATCH] events: Ensure that timers are updated without requiring read() call | From | Peter Zijlstra <> | Date | Thu, 23 Jun 2011 16:45:37 +0200 |
| |
On Thu, 2011-06-23 at 10:38 -0400, Eric B Munson wrote: > 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@mgebm.net> > > > --- > > > 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?
IIRC Stephane did something along these lines, he kept a stamp and then computed a delta in NMI context using perf_clock(). Let me try and find where that lives.
See perf_output_read().
| |