Messages in this thread | | | Date | Wed, 6 Jul 2011 19:10:15 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC] [PATCH] perf: Attaching an event to a specific PMU |
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* Robert Richter <robert.richter@amd.com> wrote:
> On 05.07.11 05:12:52, Ingo Molnar wrote: > > > > * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > > > > > Overall, my approach improves the perf design. It adds a better > > > > and more intuitve access to perf from user space with clear and > > > > common methods and interfaces. Please let me know the concerns > > > > you have. > > > > > > Its redundant, this interface ship has sailed, its not going to > > > happen. > > > > Even if we had the choice, i don't see how a /dev based enumeration > > of PMUs is in any way better than a topologically attached set of > > PMUs in /sys. > > > > This kind of structure is nice in principle: > > > > # ls -l /dev/pmu/ > > total 0 > > crw-rw---- 1 root root 254, 5 Jul 8 2011 breakpoint > > crw-rw---- 1 root root 254, 4 Jul 8 2011 cpu > > crw-rw---- 1 root root 254, 6 Jul 8 2011 proto > > crw-rw---- 1 root root 254, 1 Jul 8 2011 software > > crw-rw---- 1 root root 254, 2 Jul 8 2011 tracepoint > > > > But it should be done in /sys/. > > I have to learn yet why /dev is bad and /sys is good...
Because /sys is already there and already carries rather rich classification of various hardware components, devices and kernel subsystems.
/dev/ is mostly a flat registry of classical, unstructured devices.
> The system topology is always in /sys, also for device nodes. But > we can't get a device file descriptor from /sys. I doubt /sys is > capable to handle a device use count (need to be checked). We > actually must grab the pmu while attaching events to it. And, user > space implementation is must easier with /dev (see code in my > previous mail).
I think Peter suggested it that an open() done in /sys should give us a handle to a given event?
> My patch also includes code that creates a device class. It is also > visible in /sys/class/pmu/*.
But PMU is a very limited term: what we want is a higher level organization of 'event sources' and 'events'. Some may come from PMUs, many wont.
Thanks,
Ingo
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