linux-kernel - Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs

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Message-ID: <1273490824.5605.3379.camel@twins>
Date:	Mon, 10 May 2010 13:27:04 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"eranian@...il.com" <eranian@...il.com>,
	"Gary.Mohr@...l.com" <Gary.Mohr@...l.com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs

On Mon, 2010-05-10 at 18:26 +0800, Lin Ming wrote:

> > No, I'm assuming there is only 1 PMU per CPU. Corey is the expert on
> > crazy hardware though, but I think the sanest way is to extend the CPU
> > topology if there's more structure to it.
> 
> But our goal is to support multiple pmus, don't we need to assume there
> are more than 1 PMU per CPU?

No, because as I said, then its ambiguous what pmu you want. If you have
that, you need to extend your topology information.

Anyway, I talked with Ingo on this and he'd like to see this somewhat
extended.

Instead of a pmu_id field, which we pass into a new
perf_event_attr::pmu_id field, how about creating an event_source sysfs
class. Then each class can have an event_source_id and a hierarchy of
'generic' events.

We'd start using the PERF_TYPE_ space for this and express the
PERF_COUNT_ space in the event attributes found inside that class.

That way we can include all the existing event enumerations into this as
well.

This way we can create:

/sys/devices/system/cpu/cpuN/cpu_hardware_events 
                             cpu_hardware_events/event_source_id
                             cpu_hardware_events/cpu_cycles
                             cpu_hardware_events/instructions
                                                /...

/sys/devices/system/cpu/cpuN/cpu_raw_events
                             cpu_raw_events/event_source_id

These would match the current PERF_TYPE_* values for compatibility

For new PMUs we can start a dynamic range of PERF_TYPE_ (say at 64k but
that's not ABI and can be changed at any time, we've got u32 to play
with).

For uncore this would result in:

/sys/devices/system/node/nodeN/node_raw_events
                               node_raw_events/event_source_id

and maybe:

/sys/devices/system/node/nodeN/node_events
                               node_events/event_source_id
                               node_events/local_misses
                                          /local_hits
                                          /remote_misses
                                          /remote_hits
                                          /...

The software events and tracepoints and kprobes stuff we could hang off
of /sys/kernel/ or something

So your registration would indeed look like something:

 perf_event_register_pmu(struct pmu *pmu, int type),

where type would normally be -1 (dynamic) but would be PERF_TYPE_ for
those already laid down in ABI.

This approach will also give us a good overview
in /sys/class/event_source/, which will be a flat listing of all
existing event sources.

Does this make sense?

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