On 02/06/2014 02:35 AM, Stephane Eranian wrote: > 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().
Sorry. I forget why I used xhcg(), maybe save a few lines of code. Regards Yan, Zheng > >>>> 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/
