linux-kernel - Re: [PATCH 1/4] perf: Add memory load/store events generic code

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Date:	Wed, 06 Jul 2011 15:58:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Lin Ming <ming.m.lin@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: [PATCH 1/4] perf: Add memory load/store events generic code

On Wed, 2011-07-06 at 09:02 +1000, Paul Mackerras wrote:
> On Tue, Jul 05, 2011 at 02:03:38PM +0200, Peter Zijlstra wrote:
> > On Mon, 2011-07-04 at 10:44 +0200, Peter Zijlstra wrote:
> > > Anton, Paulus, IIRC PowerPC had some sort of Data-Source indication,
> > > would you have some docs available on the PowerPC PMU?
> > 
> > Going through
> > http://www.power.org/resources/downloads/PowerISA_V2.06B_V2_PUBLIC.pdf
> > 
> > Book III-S, Appendix B
> > 
> > I can only find the SDAR thing (which I assume is what PERF_SAMPLE_DATA
> > uses) but no mention of extra bits describing where the data was sourced
> > from. For some reason I had the impression PPC64 had the capability to
> > tell if a load/store was from/to L1/2/3/DRAM etc.
> > 
> > Now since the above document is in fact not an exhaustive spec of a
> > particular chip but more an outline of what a regular ppc64 chip should
> > have, with lots of room for implementation specific extensions it
> > doesn't say much at all.
> > 
> > So do you know of such a feature for PPC64 and if so, where's the
> > docs? :-)
> 
> Unfortunately the P7 PMU documentation is not available publicly yet. :(

Are the P6/P6+ PMU docs? That at least would give me something to look
at.

> There are events that can be used to count how many times data or
> instructions get loaded from different places in the memory
> subsystem.  There are 15 separate DATA_FROM_xxx events, for instance,
> that count things like "number of times data was loaded from L2 or L3
> cache on another chip and the cache line was in shared state".
> They're great if you want fine detail on memory traffic but perhaps
> not so good if you want a broad overview (there are separate events
> for L1 and L2 accesses and misses though).
> 
> I've attached a table of P7 PMU events.  Look for the PM_DATA_FROM_xxx
> and PM_INST_FROM_xxx events.

Ok, so those are regular events and perf covers that capability.

The thing we're talking about is Intel PEBS Load Latency/Precise Store
and AMD IBS where together with a mem op retired event (mem loads
retired for Load-Latency, mem stores retired for Precise Store) provides
an additional field describing where the load/store was sourced from.

Such additional data would require the addition of a PERF_SAMPLE_SOURCE
field or similar, for some reason or other I was under the impression
some of the PPC chips had something similar. But if not, it saves us
having to worry about that.
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