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From: Ingo Molnar <mingo@kernel.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org,
	Stephane Eranian <eranian@google.com>,
	Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page
Date: Mon, 19 Oct 2015 10:08:52 +0200	[thread overview]
Message-ID: <20151019080852.GA24924@gmail.com> (raw)
In-Reply-To: <1445001845-13688-2-git-send-email-adrian.hunter@intel.com>


* Adrian Hunter <adrian.hunter@intel.com> wrote:

> Commit b20112edeadf ("perf/x86: Improve accuracy of perf/sched clock")
> allowed the time_shift value in perf_event_mmap_page to be as much
> as 32.  Unfortunately the documented algorithms for using time_shift
> have it shifting an integer, whereas to work correctly with the value
> 32, the type must be u64.
> 
> Fix by limiting the shift to 31 and adjusting the multiplier accordingly.
> 
> Also update the documentation of perf_event_mmap_page so that new code
> based on it will be more future-proof.
> 
> Fixes: b20112edeadf ("perf/x86: Improve accuracy of perf/sched clock")
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>

Would be nice to point out via what symptoms the code misbehaves and how users 
notice.

Thanks,

	Ingo

  reply	other threads:[~2015-10-19  8:09 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-16 13:24 [PATCH 0/1] perf/x86: Fix time_shift in perf_event_mmap_page Adrian Hunter
2015-10-16 13:24 ` [PATCH 1/1] " Adrian Hunter
2015-10-19  8:08   ` Ingo Molnar [this message]
2015-10-19  8:46     ` Adrian Hunter
2015-10-19 11:21       ` Ingo Molnar
2015-10-19 11:57         ` [PATCH V2 " Adrian Hunter
2015-10-20  9:35   ` [tip:perf/core] " tip-bot for Adrian Hunter

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