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Date: Fri, 22 Apr 2011 08:19:21 GMT From: tip-bot for Ingo Molnar <mingo@...e.hu> To: linux-tip-commits@...r.kernel.org Cc: linux-kernel@...r.kernel.org, acme@...hat.com, hpa@...or.com, mingo@...hat.com, torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl, fweisbec@...il.com, ak@...ux.intel.com, tglx@...utronix.de, mingo@...e.hu Subject: [tip:perf/urgent] x86, perf event: Turn off unstructured raw event access to offcore registers Commit-ID: b52c55c6a25e4515b5e075a989ff346fc251ed09 Gitweb: http://git.kernel.org/tip/b52c55c6a25e4515b5e075a989ff346fc251ed09 Author: Ingo Molnar <mingo@...e.hu> AuthorDate: Fri, 22 Apr 2011 08:44:38 +0200 Committer: Ingo Molnar <mingo@...e.hu> CommitDate: Fri, 22 Apr 2011 10:02:53 +0200 x86, perf event: Turn off unstructured raw event access to offcore registers Andi Kleen pointed out that the Intel offcore support patches were merged without user-space tool support to the functionality: | | The offcore_msr perf kernel code was merged into 2.6.39-rc*, but the | user space bits were not. This made it impossible to set the extra mask | and actually do the OFFCORE profiling | Andi submitted a preliminary patch for user-space support, as an extension to perf's raw event syntax: | | Some raw events -- like the Intel OFFCORE events -- support additional | parameters. These can be appended after a ':'. | | For example on a multi socket Intel Nehalem: | | perf stat -e r1b7:20ff -a sleep 1 | | Profile the OFFCORE_RESPONSE.ANY_REQUEST with event mask REMOTE_DRAM_0 | that measures any access to DRAM on another socket. | But this kind of usability is absolutely unacceptable - users should not be expected to type in magic, CPU and model specific incantations to get access to useful hardware functionality. The proper solution is to expose useful offcore functionality via generalized events - that way users do not have to care which specific CPU model they are using, they can use the conceptual event and not some model specific quirky hexa number. We already have such generalization in place for CPU cache events, and it's all very extensible. "Offcore" events measure general DRAM access patters along various parameters. They are particularly useful in NUMA systems. We want to support them via generalized DRAM events: either as the fourth level of cache (after the last-level cache), or as a separate generalization category. That way user-space support would be very obvious, memory access profiling could be done via self-explanatory commands like: perf record -e dram ./myapp perf record -e dram-remote ./myapp ... to measure DRAM accesses or more expensive cross-node NUMA DRAM accesses. These generalized events would work on all CPUs and architectures that have comparable PMU features. ( Note, these are just examples: actual implementation could have more sophistication and more parameter - as long as they center around similarly simple usecases. ) Now we do not want to revert *all* of the current offcore bits, as they are still somewhat useful for generic last-level-cache events, implemented in this commit: e994d7d23a0b: perf: Fix LLC-* events on Intel Nehalem/Westmere But we definitely do not yet want to expose the unstructured raw events to user-space, until better generalization and usability is implemented for these hardware event features. ( Note: after generalization has been implemented raw offcore events can be supported as well: there can always be an odd event that is marginally useful but not useful enough to generalize. DRAM profiling is definitely *not* such a category so generalization must be done first. ) Furthermore, PERF_TYPE_RAW access to these registers was not intended to go upstream without proper support - it was a side-effect of the above e994d7d23a0b commit, not mentioned in the changelog. As v2.6.39 is nearing release we go for the simplest approach: disable the PERF_TYPE_RAW offcore hack for now, before it escapes into a released kernel and becomes an ABI. Once proper structure is implemented for these hardware events and users are offered usable solutions we can revisit this issue. Reported-by: Andi Kleen <ak@...ux.intel.com> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Arnaldo Carvalho de Melo <acme@...hat.com> Cc: Frederic Weisbecker <fweisbec@...il.com> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Link: http://lkml.kernel.org/r/1302658203-4239-1-git-send-email-andi@firstfloor.org Signed-off-by: Ingo Molnar <mingo@...e.hu> --- arch/x86/kernel/cpu/perf_event.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index eed3673a..632e5dc 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -586,8 +586,12 @@ static int x86_setup_perfctr(struct perf_event *event) return -EOPNOTSUPP; } + /* + * Do not allow config1 (extended registers) to propagate, + * there's no sane user-space generalization yet: + */ if (attr->type == PERF_TYPE_RAW) - return x86_pmu_extra_regs(event->attr.config, event); + return 0; if (attr->type == PERF_TYPE_HW_CACHE) return set_ext_hw_attr(hwc, event); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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