Sorry for double post, forgot to cc lkml...
On 07/19, Ingo Molnar wrote:
>
> * 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?
Ingo,
It seems that everybody agree with this hack but it was forgotten,
let me resend it again.
The only change is that I added the following tags:
Tested-by: David Ahern <dsah...@gmail.com>
Reviewed-and-Acked-by: Steven Rostedt <rost...@goodmis.org>
Oleg.
include/trace/events/sched.h | 22 ++++++++--------------
include/trace/ftrace.h | 33 ++++++++++++++++++++-------------
2 files changed, 28 insertions(+), 27 deletions(-)
--
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/
