Re: [rfc] Describe events in a structured way via sysfs

[Ingo Molnar]

* Lin Ming <ming.m.lin@xxxxxxxxx> wrote:

> On Tue, 2010-06-29 at 18:26 +0800, Ingo Molnar wrote:
> > * Lin Ming <ming.m.lin@xxxxxxxxx> wrote:
> > 
> > > > Also, we can (optionally) consider 'generic', subsystem level events to 
> > > > also show up under:
> > > > 
> > > >    /sys/bus/pci/drivers/i915/events/
> > > > 
> > > > This would give a model to non-device-specific events to be listed one 
> > > > level higher in the sysfs hierarchy.
> > > > 
> > > > This too would be done in the driver, not by generic code. It's generally 
> > > > the driver which knows how the events should be categorized.
> > > 
> > > This is a bit difficult. I'd like not to touch TRACE_EVENT(). [...]
> > 
> > We can certainly start with the simpler variant - it's also the more common 
> > case.
> > 
> > > [...] How does the driver know if an event is 'generic' if TRACE_EVENT is 
> > > not touched?
> > 
> > Well, it's per driver code which creates the 'events' directory anyway, so 
> > that code decides where to link things. It can link it to the per driver kobj 
> > - or to the per subsys kobj.
> > 
> > > > I'd imagine something similar for wireless drivers as well - most 
> > > > currently defined events would show up on a per device basis there.
> > > > 
> > > > Can you see practical problems with this scheme?
> > > 
> > > Not now. I may find some problems when write more detail code.
> > 
> > Ok. Feel free to post RFC patches (even if they are not fully complete yet), 
> > so that we can see how things are progressing.
> > 
> > I suspect the best approach would be to try to figure out the right sysfs 
> > placement for one or two existing driver tracepoints, so that we can see it 
> > all in practice. (Obviously any changes to drivers will have to go via the 
> > relevant driver maintainer tree(s).)
> 
> Well, take i915 tracepoints as an example, the sys structures as below
> 
> /sys/class/drm/card0/events/
> |-- i915_gem_object_bind
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_object_change_domain
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_object_clflush
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_object_create
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_object_destroy
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_object_get_fence
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_object_unbind
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_request_complete
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_request_flush
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_request_retire
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_request_submit
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_request_wait_begin
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_gem_request_wait_end
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> |-- i915_ring_wait_begin
> |   |-- enable
> |   |-- filter
> |   |-- format
> |   `-- id
> `-- i915_ring_wait_end
>     |-- enable
>     |-- filter
>     |-- format
>     `-- id
> 
> And below is the very draft patch to export i915 tracepoints in sysfs.
> Is it the right direction?

Yeah, i think so.

The per driver impact is small and to the point:

>  drivers/gpu/drm/i915/i915_drv.c |   15 +++-

>  i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  {
> -	return drm_get_dev(pdev, ent, &driver);
> +	struct kobject *kobj;
> +	struct drm_device *drm_dev;
> +	int ret;
> +
> +	ret = drm_get_dev(pdev, ent, &driver);
> +
> +	if (!ret) {
> +		drm_dev = pci_get_drvdata(pdev);
> +		kobj = &drm_dev->primary->kdev.kobj;
> +		perf_sys_register_tp(kobj, "i915");
> +	}
> +
> +	return ret;

(It could be even shorter - the same compactness comment as i made last time 
still holds for this function.)

Thanks,

	Ingo
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