Messages in this thread | | | Date | Tue, 6 Jan 2015 08:59:24 -0800 | From | Shaohua Li <> | Subject | Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO |
| |
On Tue, Jan 06, 2015 at 11:18:39AM +0100, Peter Zijlstra wrote: > On Mon, Jan 05, 2015 at 03:23:38PM -0800, Shaohua Li wrote: > > Good, it works. But the timestamp (.time_running and friends) only gets > > updated for real hardware event between context switches. For software > > event, the timestamp is initialized once, then never updated. If I use > > it to get time, I actually get CLOCK_MONOTONIC. Hardware events work > > well here, but depending on hardware event is too tricky, which I'd like > > to avoid. > > Hmm, that's an unfortunate difference in behaviour, does something like > the below cure that for you?
Yes, I tried similar here, it works perfectly. Is this a bug we will eventually fix? If yes, we will very happy to use perf for the clock_gettime things. I had some initial benchmarks which show this doesn't have noticeable performance issue. I'll do more benchamrks and report back if there are any issues.
Thanks, Shaohua
> > --- > kernel/events/core.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 4c1ee7f2bebc..0feb4e039359 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5965,11 +5965,13 @@ static void perf_swevent_del(struct perf_event *event, int flags) > static void perf_swevent_start(struct perf_event *event, int flags) > { > event->hw.state = 0; > + perf_event_update_userpage(event); > } > > static void perf_swevent_stop(struct perf_event *event, int flags) > { > event->hw.state = PERF_HES_STOPPED; > + perf_event_update_userpage(event); > } > > /* Deref the hlist from the update side */ > @@ -6410,12 +6412,14 @@ static void cpu_clock_event_start(struct perf_event *event, int flags) > { > local64_set(&event->hw.prev_count, local_clock()); > perf_swevent_start_hrtimer(event); > + perf_event_update_userpage(event); > } > > static void cpu_clock_event_stop(struct perf_event *event, int flags) > { > perf_swevent_cancel_hrtimer(event); > cpu_clock_event_update(event); > + perf_event_update_userpage(event); > } > > static int cpu_clock_event_add(struct perf_event *event, int flags) > @@ -6484,12 +6488,14 @@ static void task_clock_event_start(struct perf_event *event, int flags) > { > local64_set(&event->hw.prev_count, event->ctx->time); > perf_swevent_start_hrtimer(event); > + perf_event_update_userpage(event); > } > > static void task_clock_event_stop(struct perf_event *event, int flags) > { > perf_swevent_cancel_hrtimer(event); > task_clock_event_update(event, event->ctx->time); > + perf_event_update_userpage(event); > } > > static int task_clock_event_add(struct perf_event *event, int flags)
| |