linux-kernel - Re: [PATCH] intel_pstate: Change busy calculation to use fixed point math.

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Date:	Fri, 28 Feb 2014 14:47:41 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	dirk.brandewie@...il.com
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	rafael.j.wysocki@...el.com, gf435@....net, bp@...en8.de,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH] intel_pstate: Change busy calculation to use fixed point
 math.

On Tue, Feb 25, 2014 at 10:35:37AM -0800, dirk.brandewie@...il.com wrote:
> From: Dirk Brandewie <dirk.j.brandewie@...el.com>
> 
> Commit fcb6a15c2e Take core C0 time into account for core busy calculation.
> 
> Introduced a regression on some processor SKUs supported by
> intel_pstate. This was caused by the truncation caused by using
> integer math to calculate core busy and C0 percentages.
> 
> On a i7-4770K processor operating at 800Mhz going to 100% utilization
> the percent busy of the CPU using integer math is 22% it actually is
> 22.85%.  This value scaled to the current frequency returned 97 which
> the PID interpreted as no error and did not adjust the P state.
> 
> Tested on i7-4770K, i7-2600, i5-3230M
> 
> References:
>    https://lkml.org/lkml/2014/2/19/626
>    https://bugzilla.kernel.org/show_bug.cgi?id=70941
> 
> Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>

Thanks, this fixed the issue for me:

Tested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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