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 3.14-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-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f0fe3cd7e12d8290c82284b5c8aee723cbd0371a Mon Sep 17 00:00:00 2001
From: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
Date: Thu, 29 May 2014 09:32:23 -0700
Subject: intel_pstate: Correct rounding in busy calculation
From: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
commit f0fe3cd7e12d8290c82284b5c8aee723cbd0371a upstream.
Changing to fixed point math throughout the busy calculation in
commit e66c1768 (Change busy calculation to use fixed point
math.) Introduced some inaccuracies by rounding the busy value at two
points in the calculation. This change removes roundings and moves
the rounding to the output of the PID where the calculations are
complete and the value returned as an integer.
Fixes: e66c17683746 (intel_pstate: Change busy calculation to use fixed point math.)
Reported-by: Doug Smythies <dsmythies@xxxxxxxxx>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/cpufreq/intel_pstate.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -40,10 +40,10 @@
#define BYT_TURBO_VIDS 0x66d
-#define FRAC_BITS 6
+#define FRAC_BITS 8
#define int_tofp(X) ((int64_t)(X) << FRAC_BITS)
#define fp_toint(X) ((X) >> FRAC_BITS)
-#define FP_ROUNDUP(X) ((X) += 1 << FRAC_BITS)
+
static inline int32_t mul_fp(int32_t x, int32_t y)
{
@@ -198,7 +198,10 @@ 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));
return (signed int)fp_toint(result);
}
@@ -563,7 +566,6 @@ static inline void intel_pstate_calc_bus
core_pct = div_fp(int_tofp((sample->aperf)),
int_tofp((sample->mperf)));
core_pct = mul_fp(core_pct, int_tofp(100));
- FP_ROUNDUP(core_pct);
sample->freq = fp_toint(
mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct));
@@ -609,7 +611,7 @@ static inline int32_t intel_pstate_get_s
max_pstate = int_tofp(cpu->pstate.max_pstate);
current_pstate = int_tofp(cpu->pstate.current_pstate);
core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
- return FP_ROUNDUP(core_busy);
+ return core_busy;
}
static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)
Patches currently in stable-queue which might be from dirk.j.brandewie@xxxxxxxxx are
queue-3.14/intel_pstate-remove-unneeded-sample-buffers.patch
queue-3.14/intel_pstate-improve-initial-busy-calculation.patch
queue-3.14/intel_pstate-remove-c0-tracking.patch
queue-3.14/intel_pstate-correct-rounding-in-busy-calculation.patch
queue-3.14/intel_pstate-add-sample-time-scaling.patch
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