linux-kernel - Re: [RESEND PATCH V2 3/4] perf/x86/intel: drain PEBS buffer in event read

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Date:   Thu, 11 Jan 2018 12:10:01 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        eranian@...gle.com, ak@...ux.intel.com
Subject: Re: [RESEND PATCH V2 3/4] perf/x86/intel: drain PEBS buffer in event
 read

On Wed, Jan 10, 2018 at 09:31:56AM -0500, Liang, Kan wrote:
> 
> 
> On 1/10/2018 5:39 AM, Jiri Olsa wrote:
> > On Mon, Jan 08, 2018 at 07:15:15AM -0800, kan.liang@...el.com wrote:
> > > From: Kan Liang <kan.liang@...ux.intel.com>
> > > 
> > > When the PEBS interrupt threshold is larger than one, there is no way to
> > > get exact auto-reload times and value needed for event update unless
> > > flush the PEBS buffer.
> > > 
> > > Drain the PEBS buffer in event read when large PEBS is enabled.
> > > 
> > > For the threshold is one, even auto-reload is enabled, it doesn't need
> > > to be specially handled. Because auto-reload is only effect when event
> > > overflow. There is no overflow in event read.
> > > 
> > > Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> > > ---
> > >   arch/x86/events/intel/core.c |  9 +++++++++
> > >   arch/x86/events/intel/ds.c   | 10 ++++++++++
> > >   arch/x86/events/perf_event.h |  2 ++
> > >   3 files changed, 21 insertions(+)
> > > 
> > > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> > > index 09c26a4..bdc35f8 100644
> > > --- a/arch/x86/events/intel/core.c
> > > +++ b/arch/x86/events/intel/core.c
> > > @@ -2060,6 +2060,14 @@ static void intel_pmu_del_event(struct perf_event *event)
> > >   		intel_pmu_pebs_del(event);
> > >   }
> > > +static void intel_pmu_read_event(struct perf_event *event)
> > > +{
> > > +	if (event->attr.precise_ip)
> > > +		return intel_pmu_pebs_read(event);
> > 
> > check for (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)
> > would be more accurate?
> > 
> 
> It will narrow down the events.
> But considering the readability, I think it would be better to use
> precise_ip.The exposed functions in ds.c should be generic functions for all
> PEBS events, not specific case.
> I think _AUTO_RELOAD looks too specific.

hum, but the PEBS drain is specific just for
PERF_X86_EVENT_AUTO_RELOAD events, right?

wrt readability maybe you could add function like:
bool pebs_drain_before_read(struct perf_event *event)
{
	return event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD;
}

thanks,
jirka