linux-kernel - Re: [PATCH v2 00/14] perf, persistent: Kernel updates for perf tool integration

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Date:	Mon, 24 Jun 2013 12:24:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Robert Richter <rric@...nel.org>
Cc:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/14] perf, persistent: Kernel updates for perf tool
 integration

On Tue, Jun 11, 2013 at 06:42:26PM +0200, Robert Richter wrote:
> The basic concept is to use a pmu as an event container for persistent
> events. The pmu registers events in sysfs and provides format and
> event information for the userland. The persistent event framework
> requires to add events to the pmu dynamically.
> 
> With the information in sysfs userland knows about how to setup the
> perf_event attribute of a persistent event. Since a persistent event
> always has the persistent flag set, a way is needed to express this in
> sysfs. A new syntax is used for this. With 'attr<num>:<mask>' any bit
> in the attribute structure may be set in a similar way as using
> 'config<num>', but <num> is an index that points to the u64 value to
> change within the attribute.
> 
> For persistent events the persistent flag (bit 23 of flag field in
> struct perf_event_attr) needs to be set which is expressed in sysfs
> with "attr5:23". E.g. the mce_record event is described in sysfs as
> follows:
> 
>  /sys/bus/event_source/devices/persistent/events/mce_record:persistent,config=106
>  /sys/bus/event_source/devices/persistent/format/persistent:attr5:23
> 

Ok so it took me a little to 'get' this PMU 'abuse', but I suppose I can
go along with it ;-)

On the specifics though; it again seems to hard assume persistent events
are for tracepoints only -- either make this very explicit or remove it.
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