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Message-Id: <1277803248.5400.16.camel@minggr.sh.intel.com>
Date: Tue, 29 Jun 2010 17:20:48 +0800
From: Lin Ming <ming.m.lin@...el.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: Johannes Berg <johannes@...solutions.net>,
Peter Zijlstra <peterz@...radead.org>,
Greg KH <greg@...ah.com>,
Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Paul Mundt <lethal@...ux-sh.org>,
"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>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Will Deacon <will.deacon@....com>,
Maynard Johnson <mpjohn@...ibm.com>,
Carl Love <carll@...ibm.com>,
Kay Sievers <kay.sievers@...y.org>,
lkml <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [rfc] Describe events in a structured way via sysfs
On Tue, 2010-06-29 at 16:55 +0800, Ingo Molnar wrote:
> * Lin Ming <ming.m.lin@...el.com> wrote:
>
> > On Fri, 2010-06-25 at 01:33 +0800, Ingo Molnar wrote:
> > > * Johannes Berg <johannes@...solutions.net> wrote:
> > >
> > > > On Thu, 2010-06-24 at 11:36 +0200, Ingo Molnar wrote:
> > > >
> > > > > That's probably best achieved via a TRACE_EVENT() variant, by passing in the
> > > > > sysfs location.
> > > > >
> > > > > It might even make sense to make this a part of TRACE_EVENT() itself and make
> > > > > 'NULL' the current default, non-sysfs-enumerated behavior. That way we can
> > > > > gradually (and non-intrusively) find all the right sysfs places for events.
> > > >
> > > > No, this doesn't work. A lot of events are multi-instance. Say you have an
> > > > event for each USB device. This event would have to show up in many places
> > > > in sysfs, and each trace_foo() invocation needs to get the struct device
> > > > pointer, not just the TRACE_EVENT() definition. Additionally, to
> > > > create/destroy the sysfs pieces we need something like init_trace_foo(dev)
> > > > and destroy_trace_foo(dev) be called when the sysfs points for the device
> > > > should be created/destroyed.
> > >
> > > Yes - but even this could be expressed via TRACE_EVENT(): by giving it a
> > > device-specific function pointer and then instantiating individual events from
> > > a single, central place in sysfs.
> > >
> > > That is the place where we already know where it ends up in sysfs, and where
> > > the event-specific function can match up whether that particular node belongs
> > > to it and whether an additional event directory should be created for that
> > > particular sysfs node.
> > >
> > > > The TRACE_EVENT() just defines the template, but such multi-instance events
> > > > really should be standardised in terms of their struct device (or maybe
> > > > kobject).
> > > >
> > > > I think that needs some TRACE_DEVICE_EVENT macro that creates the required
> > > > inlines etc, and including the init/destroy that are called when the event
> > > > should show up in sysfs.
> > > >
> > > > There's no way you can have the event show up in sysfs at the right spot
> > > > with _just_ a TRACE_EVENT macro, since at define time in the header file you
> > > > don't even have a valid struct device pointer.
> > >
> > > That would be another possible way to do it - to explicitly create the events
> > > directory. It looks a bit simpler as we wouldnt have to touch TRACE_EVENT()
> > > and because it directly expresses the 'this node has an events directory'
> > > property at the place where we create the device node.
> >
> > Let me take i915 tracepoints as an example.
> > Do you mean something like below?
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > index 423dc90..9e7e4a0 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -28,6 +28,7 @@
> > */
> >
> > #include <linux/device.h>
> > +#include <linux/perf_event.h>
> > #include "drmP.h"
> > #include "drm.h"
> > #include "i915_drm.h"
> > @@ -413,7 +414,17 @@ int i965_reset(struct drm_device *dev, u8 flags)
> > static int __devinit
> > i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
> > {
> > - return drm_get_dev(pdev, ent, &driver);
> > + struct kobject *kobj;
> > + int ret;
> > +
> > + ret = drm_get_dev(pdev, ent, &driver);
> > +
> > + if (!ret) {
> > + kobj = &pdev->dev.kobj;
> > + perf_sys_register_tp(kobj, "i915");
> > + }
> > +
> > + return ret;
>
> Yeah, something like that - assuming that this means that we'll add the events
> directory to the device directory, to all the
> /sys/bus/pci/drivers/i915/*/events/ driver directories right? (i havent
> checked the DRM code)
I haven't run the code, but I think yes.
>
> Small detail, it could be written a bit more compactly, like:
Thanks for the tip.
>
> > + int ret;
> > +
> > + ret = drm_get_dev(pdev, ent, &driver);
> > + if (!ret)
> > + perf_sys_register_tp(&pdev->dev.kobj, "i915");
> > +
> > + return ret;
>
> 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().
How does the driver know if an event is 'generic' if TRACE_EVENT is not
touched?
>
> 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.
Lin Ming
>
> Ingo
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