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SubjectRe: [RFC][PATCH] perf: sysfs type id
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@infradead.org> 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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