* Oleg Nesterov <o...@redhat.com> wrote:
> Hello.
>
> The patches are the same, I only tried to update the changelogs a bit.
> I am also quoting my old email below, to explain what this hack tries
> to do.
>
> Say, "perf record -e sched:sched_switch -p1".
>
> Every task except /sbin/init will do perf_trace_sched_switch() and
> perf_trace_buf_prepare() + perf_trace_buf_submit for no reason(),
> it doesn't have a counter.
>
> So it makes sense to add the fast-path check at the start of
> perf_trace_##call(),
>
> if (hlist_empty(event_call->perf_events))
> return;
>
> The problem is, we should not do this if __task != NULL (iow, if
> DECLARE_EVENT_CLASS() uses __perf_task()), perf_tp_event() has the
> additional code for this case.
>
> So we should do
>
> if (!__task && hlist_empty(event_call->perf_events))
> return;
>
> But __task is changed by "{ assign; }" block right before
> perf_trace_buf_submit(). Too late for the fast-path check,
> we already called perf_trace_buf_prepare/fetch_regs.
>
> So. After 2/3 __perf_task() (and __perf_count/addr) is called
> when ftrace_get_offsets_##call(args) evaluates the arguments,
> and we can check !__task && hlist_empty() right after that.
>
> Oleg.
Nice improvement.
Peter, Steve, any objections?
Thanks,
Ingo
--
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/
