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From: Peter Zijlstra <peterz@infradead.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.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 V3] perf: x86: Improve accuracy of perf/sched clock
Date: Tue, 1 Sep 2015 10:57:03 +0200	[thread overview]
Message-ID: <20150901085703.GJ16853@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <55E56396.3090708@intel.com>

On Tue, Sep 01, 2015 at 11:36:38AM +0300, Adrian Hunter wrote:
> On 21/08/15 12:05, Adrian Hunter wrote:
> > When TSC is stable perf/sched clock is based on it.
> > However the conversion from cycles to nanoseconds
> > is not as accurate as it could be.  Because
> > CYC2NS_SCALE_FACTOR is 10, the accuracy is +/- 1/2048
> > 
> > The change is to calculate the maximum shift that
> > results in a multiplier that is still a 32-bit number.
> > For example all frequencies over 1 GHz will have
> > a shift of 32, making the accuracy of the conversion
> > +/- 1/(2^33).  That is achieved by using the
> > 'clocks_calc_mult_shift()' function.
> > 
> > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> 
> Ping?

I've queued it. Thanks

  reply	other threads:[~2015-09-01  8:57 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-28 21:14 [PATCH V2] perf: x86: Improve accuracy of perf/sched clock Adrian Hunter
2015-08-17  7:34 ` Adrian Hunter
2015-08-17  9:56   ` Peter Zijlstra
2015-08-20 19:31 ` Thomas Gleixner
2015-08-21  6:46   ` Adrian Hunter
2015-08-21  9:05     ` [PATCH V3] " Adrian Hunter
2015-09-01  8:36       ` Adrian Hunter
2015-09-01  8:57         ` Peter Zijlstra [this message]
2015-09-13 11:08       ` [tip:perf/core] perf/x86: " tip-bot for Adrian Hunter

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