Messages in this thread | | | Subject | Re: [patch] Performance Counters for Linux, v3 | From | Peter Zijlstra <> | Date | Fri, 12 Dec 2008 10:00:36 +0100 |
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On Fri, 2008-12-12 at 09:51 +0100, Peter Zijlstra wrote: > On Fri, 2008-12-12 at 09:35 +0100, stephane eranian wrote: > > Peter, > > > > On Fri, Dec 12, 2008 at 9:25 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > >> > + /* > > >> > + * Common hardware events, generalized by the kernel: > > >> > + */ > > >> > + PERF_COUNT_CYCLES = 0, > > >> > + PERF_COUNT_INSTRUCTIONS = 1, > > >> > + PERF_COUNT_CACHE_REFERENCES = 2, > > >> > + PERF_COUNT_CACHE_MISSES = 3, > > >> > + PERF_COUNT_BRANCH_INSTRUCTIONS = 4, > > >> > + PERF_COUNT_BRANCH_MISSES = 5, > > >> > > >> Many machines do not support these counts. For example, Niagara T1 does > > >> not have a CYCLES count. And good luck if you think you can easily come > > >> up with something meaningful for the various kind of CACHE_MISSES on the > > >> Pentium 4. Also, the Pentium D has various flavors of retired instruction > > >> count with slightly different semantics. This kind of abstraction should > > >> be done in userspace. > > > > > > I'll argue to disagree, sure such events might not be supported by any > > > particular hardware implementation - but the fact that PAPI gives a list > > > of 'common' events means that they are, well, common. So unifying them > > > between those archs that do implement them seems like a sane choice, no? > > > > > > For those archs that do not support it, it will just fail to open. No > > > harm done. > > > > > > The proposal allows for you to specify raw hardware events, so you can > > > just totally ignore this part of the abstraction. > > > > > I believe the cache related events do not belong in here. There is no definition > > for them. You don't know what cache miss level, what kind of access. You cannot > > do this even on Intel Core processors. > > I might agree with that, perhaps we should model this to the common list > PAPI specifies?
http://icl.cs.utk.edu/projects/papi/files/html_man3/papi_presets.html
Has a lot of cache events.
And I can see the use of a set without the L[123] in there, which would signify either all or the lack of more specific knowledge. Like with PAPI its perfectly fine to not support these common events on a particular hardware platform.
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