This is a note to let you know that I've just added the patch titled
intel_pstate: Correct rounding in busy calculation
to the 3.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
intel_pstate-correct-rounding-in-busy-calculation.patch
and it can be found in the queue-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 51d211e9c334b9eca3505f4052afa660c3e0606b Mon Sep 17 00:00:00 2001
From: Doug Smythies <doug.smythies@xxxxxxxxx>
Date: Tue, 17 Jun 2014 13:36:10 -0700
Subject: intel_pstate: Correct rounding in busy calculation
From: Doug Smythies <doug.smythies@xxxxxxxxx>
commit 51d211e9c334b9eca3505f4052afa660c3e0606b upstream.
There was a mistake in the actual rounding portion this previous patch:
f0fe3cd7e12d (intel_pstate: Correct rounding in busy calculation) such that
the rounding was asymetric and incorrect.
Severity: Not very serious, but can increase target pstate by one extra value.
For real world work flows the issue should self correct (but I have no proof).
It is the equivalent of different PID gains for positive and negative numbers.
Examples:
-3.000000 used to round to -4, rounds to -3 with this patch.
-3.503906 used to round to -5, rounds to -4 with this patch.
Fixes: f0fe3cd7e12d (intel_pstate: Correct rounding in busy calculation)
Signed-off-by: Doug Smythies <dsmythies@xxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/cpufreq/intel_pstate.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -200,10 +200,7 @@ static signed int pid_calc(struct _pid *
pid->last_err = fp_error;
result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm;
- if (result >= 0)
- result = result + (1 << (FRAC_BITS-1));
- else
- result = result - (1 << (FRAC_BITS-1));
+ result = result + (1 << (FRAC_BITS-1));
return (signed int)fp_toint(result);
}
Patches currently in stable-queue which might be from doug.smythies@xxxxxxxxx are
queue-3.15/intel_pstate-correct-rounding-in-busy-calculation.patch
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