On Wed, Feb 5, 2014 at 6:55 PM, Peter Zijlstra <pet...@infradead.org> wrote: > On Wed, Feb 05, 2014 at 06:19:27PM +0100, Stephane Eranian wrote: >> On Fri, Jan 3, 2014 at 6:48 AM, Yan, Zheng <zheng.z....@intel.com> wrote: >> > If two tasks were both forked from the same parent task, Events in their >> > perf >> > task contexts can be the same. Perf core optimizes context switch oout in >> > this >> > case. >> > >> > Previous patch inroduces pmu specific data. The data is task specific, so >> > we >> > should switch the data even when context switch is optimized out. >> > >> Reviwed-by: Stephane Eranian <eran...@google.com> > > You should look again.. that xchg() is an atomic op and a total waste of > time since the assignment back onto ctx->task_ctx_data is non-atomic. > > Complete fail there. > I admit, it was not clear to me why the xchg().
>> > Signed-off-by: Yan, Zheng <zheng.z....@intel.com> >> > --- >> > kernel/events/core.c | 2 ++ >> > 1 file changed, 2 insertions(+) >> > >> > diff --git a/kernel/events/core.c b/kernel/events/core.c >> > index b6650ab..d6d8dea 100644 >> > --- a/kernel/events/core.c >> > +++ b/kernel/events/core.c >> > @@ -2319,6 +2319,8 @@ static void perf_event_context_sched_out(struct >> > task_struct *task, int ctxn, >> > next->perf_event_ctxp[ctxn] = ctx; >> > ctx->task = next; >> > next_ctx->task = task; >> > + ctx->task_ctx_data = xchg(&next_ctx->task_ctx_data, >> > + ctx->task_ctx_data); >> > do_switch = 0; >> > >> > perf_event_sync_stat(ctx, next_ctx); >> > -- >> > 1.8.4.2 >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
