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

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Date:	Tue, 11 May 2010 11:12:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"eranian@...il.com" <eranian@...il.com>,
	"Gary.Mohr@...l.com" <Gary.Mohr@...l.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>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <carll@...ibm.com>
Subject: Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs

On Tue, 2010-05-11 at 17:03 +0800, Lin Ming wrote:
> On Tue, 2010-05-11 at 16:50 +0800, Peter Zijlstra wrote:
> > On Tue, 2010-05-11 at 16:20 +0800, Lin Ming wrote:
> > 
> > > How will this sysfs interface be used for userspace tool?
> > > 
> > >  /sys/devices/system/node/nodeN/node_events
> > >                                node_events/event_source_id
> > > 
> > >                                node_events/local_misses/event_id
> > >                                           /local_hits/event_id
> > >                                           /remote_misses/event_id
> > >                                           /remote_hits/event_id
> > > 
> > > For example, to monitor node event local_misses on node 0, does it work
> > > as below?
> > > 
> > > 1. perf top -e local_misses -n 0 (-n 0 means node 0)
> > > 
> > > 2. read /sys/devices/system/node/node0/node_events/event_source_id to
> > > get the pmu_id
> > > 
> > > 3. read /sys/devices/system/node/node0/node_events/local_misses/event_id
> > > to get the event_id
> > > 
> > > 4. event_attr::pmu_id=pmu_id, event::config=event_id
> > > 
> > > 5. other setting...
> > > 
> > > 6. call syscall perf_event_open(....)
> > 
> > No, you'll use event_source_id as perf_event_attr::type, use event_id as
> > perf_event_attr::config and then use a cpu-wide counter on a cpu
> > contained in node0.
> 
> Is event_source_id a link to event_source class?

No its an attribute of said class.

> For example, 2 event sources on Nehalem
> /sys/class/event_sources/core_pmu
> /sys/class/event_sources/uncore_pmu
> 
> Then,
> /sys/devices/system/node/nodeN/node_events/event_source_id is a link
> to /sys/class/event_sources/uncore_pmu.

> /sys/devices/system/cpu/cpuN/cpu_hardware_events/event_source_id is a
> link to /sys/class/event_sources/core_pmu.

The other way around, look in /sys/class/*/, they're all symlinks.

> And, the event_source_id
> #cat /sys/class/event_sources/core_pmu
> 0

> #cat /sys/class/event_sources/uncore_pmu
> 1

You can't cat a directory. You'd cat something
like: /sys/class/event_sources/core_pmu/event_source_id

And they would contain PERF_TYPE_* like things.

So for the current CPU PMUs we'd already create 3 event classes,
cpu_hw_events, cpu_hw_cache_events, cpu_raw_events, with resp.
event_source_id of 0, 3 and 4.

The new PMUs will use a dynamic range that starts at PERF_TYPE_MAX.
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