[CPUFREQ] Measure transition latency at driver initialization
The attached patch introduces runtime latency measurement for ICH[234]
based chipsets instead of using CPUFREQ_ETERNAL. It includes
some sanity checks in case the measured value is out of range and
assigns a safe value of 500uSec that should still be enough on
problematics chipsets (current testing report values ~200uSec). The
measurement is currently done in speedstep_get_freqs in order to avoid
further unnecessary transitions and in the hope it'll come handy for SMI
also.
Signed-off-by: Mattia Dongili <malattia@linux.it>
Acked-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Dave Jones <davej@redhat.com>
speedstep-ich.c | 4 ++--
speedstep-lib.c | 32 +++++++++++++++++++++++++++++++-
speedstep-lib.h | 1 +
speedstep-smi.c | 1 +
4 files changed, 35 insertions(+), 3 deletions(-)
diff --git a/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c b/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c
index d368b3f..7c47005 100644
--- a/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c
+++ b/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c
@@ -320,11 +320,13 @@
unsigned int speedstep_get_freqs(unsigned int processor,
unsigned int *low_speed,
unsigned int *high_speed,
+ unsigned int *transition_latency,
void (*set_state) (unsigned int state))
{
unsigned int prev_speed;
unsigned int ret = 0;
unsigned long flags;
+ struct timeval tv1, tv2;
if ((!processor) || (!low_speed) || (!high_speed) || (!set_state))
return -EINVAL;
@@ -337,7 +339,7 @@
return -EIO;
dprintk("previous speed is %u\n", prev_speed);
-
+
local_irq_save(flags);
/* switch to low state */
@@ -350,8 +352,17 @@
dprintk("low speed is %u\n", *low_speed);
+ /* start latency measurement */
+ if (transition_latency)
+ do_gettimeofday(&tv1);
+
/* switch to high state */
set_state(SPEEDSTEP_HIGH);
+
+ /* end latency measurement */
+ if (transition_latency)
+ do_gettimeofday(&tv2);
+
*high_speed = speedstep_get_processor_frequency(processor);
if (!*high_speed) {
ret = -EIO;
@@ -369,6 +380,25 @@
if (*high_speed != prev_speed)
set_state(SPEEDSTEP_LOW);
+ if (transition_latency) {
+ *transition_latency = (tv2.tv_sec - tv1.tv_sec) * USEC_PER_SEC +
+ tv2.tv_usec - tv1.tv_usec;
+ dprintk("transition latency is %u uSec\n", *transition_latency);
+
+ /* convert uSec to nSec and add 20% for safety reasons */
+ *transition_latency *= 1200;
+
+ /* check if the latency measurement is too high or too low
+ * and set it to a safe value (500uSec) in that case
+ */
+ if (*transition_latency > 10000000 || *transition_latency < 50000) {
+ printk (KERN_WARNING "speedstep: frequency transition measured seems out of "
+ "range (%u nSec), falling back to a safe one of %u nSec.\n",
+ *transition_latency, 500000);
+ *transition_latency = 500000;
+ }
+ }
+
out:
local_irq_restore(flags);
return (ret);