Re: [RFC][PATCH] perf: sysfs type id

[Corey Ashford]

On 11/10/2010 01:05 PM, Peter Zijlstra wrote:
> On Wed, 2010-11-10 at 21:53 +0100, Stephane Eranian wrote:
> > On Wed, Nov 10, 2010 at 9:32 PM, Peter Zijlstra<peterz@xxxxxxxxxxxxx>  wrote:
> > > On Wed, 2010-11-10 at 21:08 +0100, Stephane Eranian wrote:
> > > > Would that be by passing the full filename to the tool?
> > >
> > > possible, or something like<pmu-name>:<event-name>, cpu:cycles would
> > > map to /sys/class/pmu/cpu/events/cycles (given the previous patch).
> > Ok, but I think you're proposal is missing one bit. You are addressing
> > the class (or type) of PMU, but you are not addressing the naming of
> > an instance.
> >
> > Let's take an example, suppose you have counters on a graphic card.
> > Your system has two such graphic cards. In your scheme you would
> > end up with a sys/class/pmu/gfx/.....
> >
> > But now, suppose I want to count cycles on the first graphic card.
> > Seems to me you need to expose the instances as well. The instance
> > number needs to be passed in the attr struct somehow.
> >
> > You can either create multiple subdir under gfx, or have this info somewhere
> > else in the sysfs tree, if people really care about class vs. instance.
> >
> > I can see users doing:
> > $ perf stat -e gfx@1::cycles ...  ->  sys/class/gfx/1/event/cycles
> >
> > The reason I am using :: here is because libpfm4 is already using
> > this as a separator for PMU type vs. event.
>
>
> right, so the idea is to have these pmu devices hooked into the existing
> sysfs topology, my proposed patch misses that bit because I wanted to
> get something out before having to dig through the topology code trying
> to figure out how all that works.
>
> So the 'cpu' pmu device would be linked from:
>
>    /sys/devices/system/cpu/pmu ->  /sys/class/pmu/cpu
>
> and gfx things would be linked like:
>
>    /sys/devices/pci0000:00/0000:00:1e.0/0000:0b:01.0/drm/card0/pmu ->  /sys/class/pmu/radeon0

I don't understand the /sys/devices tree much (I will read up on it), 
but this idea looks good to me.

To clarify my understanding a bit and taking the gfx example, in the 
path /sys/class/pmu/radeon0, is the '0' here denoting the 0'th radeon 
chip in the system, or the radeon model number?  I would assume the 0'th 
chip.

So if I assume that now points to a unique radeon chip in the system, 
underneath /sys/class/pmu/radeon0 will be a structure something like:

radeon0/
	event/
		evt0
		..
		evtn

And if there is a second radeon chip, there would be a nearly identical 
tree:

radeon1/
	event/
		evt0
		..
		evtn

Is that correct?

Some of these events may need modifiers / attributes / umasks... 
whatever you want to call them.  And they may need more than one each, 
and they may vary from event to event.  So to add to the hierarchy,
we'd have:

radeon0/
    type (for attr.type)
    event/
        evt0/
            id (a base number for attr.config)
            description (text file - but could be CONFIG_*'d out)
            modifiers/
                mod0/
                    formula (some ascii syntax for describing how
                             to set .config and/or .config_extra
                             with this modifer's value)
                    description (text - can configure out)
                    constraints (some ascii syntax for describing
                                 the values mod0 can take on)
                ..
                modn/
        ..
	evtn/

And this would be replicated for radeon1..n

Maybe all of the "event" directories could be soft links to a common
radeon<model_number> event directory.

When you fully specify an event, you have something like:

/sys/devices/pci0000:00/0000:00:1e.0/0000:0b:01.0/drm/card0/pmu/<event>[:<modifier>=nnn:...]

So it wouldn't end up being strictly a sysfs path anymore, and perf 
would have a bit of parsing work to do, to evaluate the modifiers, using 
the info from constraints, and construct the .type, .config, and 
.config_extra fields using formula.

Or maybe you have some other structure in mind?

- Corey
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