From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Vince Weaver <vincent.weaver@maine.edu>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
torvalds@linux-foundation.org, eranian@google.com,
acme@redhat.com, hpa@zytor.com,
alexander.shishkin@linux.intel.com, mingo@kernel.org,
jolsa@redhat.com, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] perf/x86/intel: Disable userspace RDPMC usage for large PEBS
Date: Mon, 12 Mar 2018 10:08:09 -0400 [thread overview]
Message-ID: <c346074e-111f-da65-68c9-b24253a1f5fa@linux.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1803091407080.4834@macbook-air>
On 3/9/2018 2:10 PM, Vince Weaver wrote:
> On Fri, 9 Mar 2018, Peter Zijlstra wrote:
>
>> On Fri, Mar 09, 2018 at 09:31:11AM -0500, Vince Weaver wrote:
>>> On Fri, 9 Mar 2018, tip-bot for Kan Liang wrote:
>>>
>>>> Commit-ID: 1af22eba248efe2de25658041a80a3d40fb3e92e
>>>> Gitweb: https://git.kernel.org/tip/1af22eba248efe2de25658041a80a3d40fb3e92e
>>>> Author: Kan Liang <kan.liang@linux.intel.com>
>>>> AuthorDate: Mon, 12 Feb 2018 14:20:35 -0800
>>>> Committer: Ingo Molnar <mingo@kernel.org>
>>>> CommitDate: Fri, 9 Mar 2018 08:22:23 +0100
>>>>
>>>> perf/x86/intel: Disable userspace RDPMC usage for large PEBS
>>>>
>>>
>>>
>>> So this whole commit log is about disabling RDPMC usage for "large PEBS"
>>> but the actual change disables RDPMC if "PERF_X86_EVENT_FREERUNNING"
>>>
>>> Either the commit log is really misleading, or else a poor name was chosen
>>> for this feature.
>>
>> Its the same thing, and yes that might want renaming I suppose.
>
> I apologize for noticing these things so late in the game, but I haven't
> had time to keep up with a full lkml feed recently so I only see these
> things once I'm CC'd on them.
>
> So to summarize this: rdpmc is only disabled on a per-event basis, and
> only if that event is doing multi-pebs sampling?
>
If the event can do multi-pebs sampling, the rdpmc will be disabled.
Other events which cannot do multi-pebs will not be impacted.
To enable multi-pebs sampling for event, it requires a fixed period.
It doesn't support callgraph. For older platform (before SKL), it
doesn't support time stamp.
Thanks,
Kan
> If that's true, then I don't think I have an issue with this.
>
> We finally got rdpmc support in a released PAPI, and it is a massive
> improvement when self-monitoring (even moreso if KPTI is enabled) so I was
> just trying to make sure this wouldn't suddenly disable rdpmc out from
> under us.
>
> Vince
>
next prev parent reply other threads:[~2018-03-12 14:08 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-12 22:20 [PATCH V4 0/5] bugs fix for auto-reload mmap read and rdpmc read kan.liang
2018-02-12 22:20 ` [PATCH V4 1/5] perf/x86/intel: Fix event update for auto-reload kan.liang
2018-02-17 6:21 ` [perf/x86/intel] 41e062cd2e: WARNING:at_arch/x86/events/intel/ds.c:#intel_pmu_save_and_restart_reload kernel test robot
2018-02-17 6:21 ` kernel test robot
2018-02-19 12:44 ` Peter Zijlstra
2018-02-19 12:44 ` Peter Zijlstra
2018-02-20 18:59 ` Liang, Kan
2018-02-20 18:59 ` Liang, Kan
2018-03-09 9:08 ` [tip:perf/core] perf/x86/intel: Properly save/restore the PMU state in the NMI handler tip-bot for Kan Liang
2018-02-21 10:32 ` [PATCH V4 1/5] perf/x86/intel: Fix event update for auto-reload Peter Zijlstra
2018-02-21 13:43 ` Liang, Kan
2018-02-21 13:45 ` Peter Zijlstra
2018-03-09 9:08 ` [tip:perf/core] " tip-bot for Kan Liang
2018-02-12 22:20 ` [PATCH V4 2/5] perf/x86: Introduce read function for x86_pmu kan.liang
2018-03-09 9:09 ` [tip:perf/core] perf/x86: Introduce a ->read() callback in 'struct x86_pmu' tip-bot for Kan Liang
2018-02-12 22:20 ` [PATCH V4 3/5] perf/x86/intel/ds: Introduce read function for auto-reload event kan.liang
2018-03-09 9:09 ` [tip:perf/core] perf/x86/intel/ds: Introduce ->read() function for auto-reload events and flush the PEBS buffer there tip-bot for Kan Liang
2018-02-12 22:20 ` [PATCH V4 4/5] perf/x86/intel: Fix pmu read for auto-reload kan.liang
2018-03-09 9:10 ` [tip:perf/core] perf/x86/intel: Fix PMU " tip-bot for Kan Liang
2018-02-12 22:20 ` [PATCH V4 5/5] perf/x86: Fix: disable userspace RDPMC usage for large PEBS kan.liang
2018-03-09 9:10 ` [tip:perf/core] perf/x86/intel: Disable " tip-bot for Kan Liang
2018-03-09 14:31 ` Vince Weaver
2018-03-09 17:42 ` Peter Zijlstra
2018-03-09 18:53 ` Liang, Kan
2018-03-09 19:10 ` Vince Weaver
2018-03-12 14:08 ` Liang, Kan [this message]
2018-03-20 11:15 ` [tip:perf/urgent] " tip-bot for Kan Liang
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