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

[Ingo Molnar]

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

> 
> > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > 
> > > On Thu, 2010-05-20 at 16:12 -0700, Greg KH wrote:
> > 
> > > > How deep in the device tree are you really going to be
> > > > caring about?  It sounds like the large majority of
> > > > events are only going to be coming from the "system"
> > > > type objects (cpu, nodes, memory, etc.) and very few
> > > > would be from things that we consider a 'struct
> > > > device' today (like a pci, usb, scsi, or input, etc.)
> > >
> > > The general noise I hear from the hardware people is
> > > that we'll see more and more device-level stuff - bus
> > > bridges/controller and actual devices (GPUs, NICs etc.)
> > > will be wanting to export performance metrics.
> > 
> > There's (much) more:
> > 
> >  - laptops want to provide power level/usage metrics,
> > 
> >  - we could express a lot of special, lower level
> >   (transport specific) disk IO stats via events as well -
> >   without having to push those stats to a higher level
> >   (where it might not make sense). Currently such kinds
> >   of stats/metrics are very device/subsystem specific
> >   way, if they are provided at all.
> > 
> > Also, we already have quite a few per device tracepoints
> > upstream. Here are a few examples:
> > 
> >  - GPU tracepoints (trace_i915_gem_request_submit(), etc.)
> >  - WIFI tracepoints (trace_iwlwifi_dev_ioread32(), etc.)
> >  - block tracepoints (trace_block_bio_complete())
> > 
> > So these would be attached to:
> > 
> >  # GEM events of drm/card0:
> >  /sys/devices/pci0000:00/0000:00:02.0/drm/card0/events/i915_gem_request_submit/
> > 
> >  # Wifi-ioread events of wlan0:
> >  /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlan0/events/iwlwifi_dev_ioread32/
> > 
> >  # whole sdb disk events:
> >  /sys/block/sdb/events/block_bio_complete/
> > 
> >  # sdb1 partition events:
> >  /sys/block/sdb/sdb1/events/block_bio_complete/
> > 
> 
> The difficulty is how to know where each event should be attached to.
> 
> struct ftrace_event_call *call;
> 
> for_each_event(call, __start_ftrace_events, __stop_ftrace_events) {
> 	/* where will this event be attached to?  */
> }
> 
> Any idea?

Well, it cannot be automatic - for each subsystem it's a different sysfs 
point. So it has to be specified in the TRACE_EVENT() definition or so.

	Ingo
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