Messages in this thread |  | | | Date | Tue, 6 Dec 2011 11:14:14 -0800 | | Subject | Re: [PATCH 00/12] perf_events: add support for sampling taken branches (v2) | | From | Stephane Eranian <> |
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On Tue, Dec 6, 2011 at 3:03 AM, Peter Zijlstra <peterz@infradead.org> wrote: > On Tue, 2011-12-06 at 09:49 +0000, Will Deacon wrote: >> On Mon, Dec 05, 2011 at 10:39:26PM +0000, Peter Zijlstra wrote: >> > On Fri, 2011-10-14 at 14:37 +0200, Stephane Eranian wrote: >> > > This patchset adds an important and useful new feature to >> > > perf_events: branch stack sampling. In other words, the >> > > ability to capture taken branches into each sample. >> > > >> > Other than the few comments given it all looks good. My main worry is >> > the Intel only aspect, I'd really love for there to be another platform >> > that could implement at least part of this. >> >> I discussed this with Stephane in Prague and, although it would be lovely to >> have this on ARM, we simply don't have the hardware to do it. So the nature >> of series does seem to be x86-centric unless there's way to do a watered >> down version in software. > > The only way to do this in software would be like > CONFIG_PROFILE_ALL_BRANCHES and that's horrid (and kernel only). > > But there's more than Intel & ARM, but it looks like PPC doesn't have > this either and I suspect MIPS and SPARC don't either, which doesn't > leave us with much else. > There is a hardware branch buffer on all Itanium processors. You can find the description for the McKinley implementation (Itanium2) branch buffer in section 10.3.9 from: http://download.intel.com/design/Itanium2/manuals/25111003.pdf
> So I guess we should just go ahead and merge this and hope more hardware > grows this feature in a compatible enough manner.
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