> -----Original Message----- > From: Andi Kleen [mailto:[email protected]] > Sent: Monday, March 30, 2015 1:26 PM > To: Liang, Kan > Cc: Peter Zijlstra; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected] > Subject: Re: [PATCH V5 4/6] perf, x86: handle multiple records in PEBS > buffer > > > > - its possible (and harmless) for the status field to contain set bits > > > for !PEBS events -- the proposed code is buggy here. > > I will fix it. > > > - its possible to have multiple PEBS bits set even though the event > > > really only was for a single event -- if you count everything with > > > multiple PEBS bits set as a collision you're counting wrong. > > > > > > > In what situation multiple PEBS bits was set for a single event? > > Could you please give me an example? > > The field in the PEBS record is just a copy of GLOBAL_STATUS (minus some > extra bits), so if there were already bits in GLOBAL_STATUS that haven't > been cleared yet you may see multiple bits > > In a proper configuration this should be rare, as we expect the events to > be different and run on different effective frequencies, so > GLOBAL_STATUS should be already cleared.
The case you mentioned has already covered in the description. I tried both multiple different events and multiple same events. As you said, the collision for multiple different events is rare. The collision for multiple same events is very high, but it's not a useful configuration As my understanding, Peter means the multiple PEBS bits could be set when sampling only one single event. Peter, could you please clarify? Thanks, Kan > > -Andi > > -- > [email protected] -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
