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From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Gasparini <stephane.gasparini@linux.intel.com>
Cc: Len Brown <lenb@kernel.org>,
	x86@kernel.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org, Len Brown <len.brown@intel.com>
Subject: Re: [PATCH] x86: Calculate MHz using APERF/MPERF for cpuinfo and scaling_cur_freq
Date: Fri, 1 Apr 2016 10:29:23 +0200	[thread overview]
Message-ID: <20160401082923.GH11035@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160401082323.GE3448@twins.programming.kicks-ass.net>

On Fri, Apr 01, 2016 at 10:23:23AM +0200, Peter Zijlstra wrote:
> 
> Trim your emails
> 
> On Fri, Apr 01, 2016 at 10:16:42AM +0200, Stephane Gasparini wrote:
> 
> > > That means these delta's can be arbitrarily large, in fact the MSRs can
> > > have wrapped however many times.
> > 
> > 64 bits is 18 446 744 073 709 551 615
> > 
> > so even assuming a 10 GHz frequency if my math are good this is more than
> > 58 years before the MSR wrap around, assuming the device ran always at max
> > freq.
> 
> fair enough.. but going with 10Ghz, cpu_khz would be 10e6 ~ 33 bits,

I can't do maths this morning; 23 bits

> which effectively reduces the wrap/overflow time to just 31 bits, which
> per that frequency is just ~1/4th of a second.

41 giving lots more, but a reasonable time to wrap/overflow.

  reply	other threads:[~2016-04-01  8:29 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <6e0c25e64e0fb65a42dfc63ad5f660302e07cd87.1459485198.git.len.brown@intel.com>
2016-04-01  4:37 ` [PATCH] x86: Calculate MHz using APERF/MPERF for cpuinfo and scaling_cur_freq Len Brown
2016-04-01  7:56   ` [PATCH] x86: Calculate MHz using APERF/MPERF for cpuinfo and scaling_cur_freqy Thomas Gleixner
2016-04-01  8:03   ` [PATCH] x86: Calculate MHz using APERF/MPERF for cpuinfo and scaling_cur_freq Peter Zijlstra
2016-04-01  8:16     ` Stephane Gasparini
2016-04-01  8:23       ` Peter Zijlstra
2016-04-01  8:29         ` Peter Zijlstra [this message]
2016-04-01  9:30           ` Stephane Gasparini
2016-04-01  9:38             ` Peter Zijlstra
2016-04-01  9:50             ` Borislav Petkov
2016-04-02  5:22               ` Len Brown
2016-04-01  8:16   ` Peter Zijlstra
2016-04-24 16:38   ` Pavel Machek

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