Messages in this thread - First message in thread
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- "Yan, Zheng"
- Stephane Eranian
- Stephane Eranian
| | | Date | Thu, 06 Feb 2014 10:08:30 +0800 | From | "Yan, Zheng" <> | Subject | Re: [PATCH 06/14] perf, core: always switch pmu specific data during context switch |
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On 02/06/2014 02:35 AM, Stephane Eranian wrote: > On Wed, Feb 5, 2014 at 6:55 PM, Peter Zijlstra <peterz@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.yan@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 <eranian@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.yan@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 >>>>
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