linux-kernel - Re: [PATCH V8 7/8] perf, x86: introduce PERF_RECORD_LOST

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Message-ID: <20150507135822.GU21418@twins.programming.kicks-ass.net>
Date:	Thu, 7 May 2015 15:58:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"mingo@...nel.org" <mingo@...nel.org>,
	"acme@...radead.org" <acme@...radead.org>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 7/8] perf, x86: introduce PERF_RECORD_LOST_SAMPLES

On Thu, May 07, 2015 at 01:56:09PM +0000, Liang, Kan wrote:
> 
> > 
> > 
> > So I changed it slightly to the below; changes are:
> > 
> >  - record 'lost' events to all set bits; after all we really do not
> >    know which event this sample belonged to, only logging to the first
> >    set bit seems 'wrong'.
> 
> If so, the same dropped sample will be count multiple times. It's hard to know
> the exact number of dropped samples.

OTOH if the events are from different consumers, they might think there
are no samples lost, while in fact there are.
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