From: Andi Kleen <ak@linux.intel.com>
To: kan.liang@linux.intel.com
Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
linux-kernel@vger.kernel.org, tglx@linutronix.de,
jolsa@redhat.com, eranian@google.com
Subject: Re: [PATCH V2 4/4] perf/x86: fix: disable userspace RDPMC usage for large PEBS
Date: Wed, 20 Dec 2017 13:41:47 -0800 [thread overview]
Message-ID: <20171220214147.GJ25156@tassilo.jf.intel.com> (raw)
In-Reply-To: <1513798971-4257-5-git-send-email-kan.liang@linux.intel.com>
On Wed, Dec 20, 2017 at 11:42:51AM -0800, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
>
> The userspace RDPMC usage never works for large PEBS since the large
> PEBS is introduced by
> commit b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt
> handling (large PEBS interrupt threshold)")
>
> When the PEBS interrupt threshold is larger than one, there is no way to
> get exact auto-reload times and value for userspace RDPMC.
>
> Disable the userspace RDPMC usage when large PEBS is enabled.
The only drawback is that the event wraps quickly. I suspect in many
cases it's still usable for measuring short regions.
I wouldn't force disable it, just let the users deal with it.
-Andi
next prev parent reply other threads:[~2017-12-20 21:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 19:42 [PATCH V2 0/4] bug fix mmap read and rdpmc read in " kan.liang
2017-12-20 19:42 ` [PATCH V2 1/4] perf/x86/intel: fix event update for auto-reload kan.liang
2017-12-20 19:42 ` [PATCH V2 2/4] perf/x86: introduce read function for x86_pmu kan.liang
2017-12-20 19:42 ` [PATCH V2 3/4] perf/x86/intel: drain PEBS buffer in event read kan.liang
2017-12-20 19:42 ` [PATCH V2 4/4] perf/x86: fix: disable userspace RDPMC usage for large PEBS kan.liang
2017-12-20 21:41 ` Andi Kleen [this message]
2017-12-20 22:05 ` Liang, Kan
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