linux-kernel - RE: [PATCH V6 4/6] perf, x86: handle multiple records in PEBS buffer

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F077017CB364@SHSMSX103.ccr.corp.intel.com>
Date:	Fri, 17 Apr 2015 12:50:33 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"acme@...radead.org" <acme@...radead.org>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>
Subject: RE: [PATCH V6 4/6] perf, x86: handle multiple records in PEBS buffer



> >
> >  A) the CTRn value reaches 0:
> >     - the corresponding bit in GLOBAL_STATUS gets set
> >     - we start arming the hardware assist
> >
> >     < some unspecified amount of time later --
> >         this could cover multiple events of interest >
> >
> >  B) the hardware assist is armed, any next event will trigger it
> >
> >  C) a matching event happens:
> >     - the hardware assist triggers and generates a PEBS record
> >       this includes a copy of GLOBAL_STATUS at this moment
> >     - if we auto-reload we (re)set CTRn
> 
> Is this actually true? Do we reload here or on A ?
> 

Yes, on C.
According to SDM Volume 3, 18.7.1.1, the reset value will be
loaded after each PEBS record is written, which is done
by hw assist.


> >     - we clear the relevant bit in GLOBAL_STATUS
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