On Thu, 16 Jan 2014, Peter Zijlstra wrote:
> > > retry++;
> > > __asm__ __volatile__(
> > > @@ -217,6 +220,7 @@ static void speedstep_set_state(unsigned int state)
> > >
> > > /* enable IRQs */
> > > local_irq_restore(flags);
> > > + preempt_enable();
> > >
> > > if (new_state == state)
> > > pr_debug("change to %u MHz succeeded after %u tries "
> >
> > You need also preempt_disable/enable in speedstep_get_freqs.
>
> Argh I see, this is really horrid.
>
>
> Anyway, its Rafael's call, its his subsystem he gets to fix it when it
> explodes.
>
> /me shudders
speedstep_get_freqs disables the interrupts to measure the transition
latency. It is called from speedstep-ich.c (that requires the latency) and
from speedstep-smi.c (that passes NULL as a pointer to latency, because it
doesn't need it).
So, you could disable interrupts in speedstep_get_freqs only when the
transition_latency pointer is non-NULL.
I think speedstep_set_state doesn't need to disable interrupts at all -
all that it does is one "out" instruction, you don't need to synchronize
that "out" instruction with anything, so there is no need to disable
interrupts. Or - does some specification say that interrupts must be
disabled there?
I am sending this patch to clean up the mess to be applied on the top of
my previous patch.
Mikulas
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Subject: speedstep: clean up interrupt disabling
This patch cleans up interrupt disabling in speedstep-smi and
speedstep-lib.
speedstep_get_freqs in speedstep-lib may be called from speedstep-smi or
speedstep-ich. When it is called from speedstep-ich, it needs to calculate
transition latency. When it is called from speedstep-smi, transition
latency doesn't have to be calculated.
The function speedstep_set_state in speedstep-smi needs to enable
interrupts. Previously it enabled interrupts even if it was called with
disabled interrupts, but it is dirty.
This patch changes speedstep_get_freqs so that it disables interrupts only
when it is called from speedstep-ich and when it is measuring the
transition latency. This avoids much of the code dirtiness.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/cpufreq/speedstep-lib.c | 13 ++++++-------
drivers/cpufreq/speedstep-smi.c | 11 ++++-------
2 files changed, 10 insertions(+), 14 deletions(-)
Index: linux-3.4.75/drivers/cpufreq/speedstep-lib.c
===================================================================
--- linux-3.4.75.orig/drivers/cpufreq/speedstep-lib.c 2014-01-16 18:51:16.000000000 +0100
+++ linux-3.4.75/drivers/cpufreq/speedstep-lib.c 2014-01-16 18:51:22.000000000 +0100
@@ -400,9 +400,6 @@ unsigned int speedstep_get_freqs(enum sp
pr_debug("previous speed is %u\n", prev_speed);
- preempt_disable();
- local_irq_save(flags);
-
/* switch to low state */
set_state(SPEEDSTEP_LOW);
*low_speed = speedstep_get_frequency(processor);
@@ -414,15 +411,19 @@ unsigned int speedstep_get_freqs(enum sp
pr_debug("low speed is %u\n", *low_speed);
/* start latency measurement */
- if (transition_latency)
+ if (transition_latency) {
+ local_irq_save(flags);
do_gettimeofday(&tv1);
+ }
/* switch to high state */
set_state(SPEEDSTEP_HIGH);
/* end latency measurement */
- if (transition_latency)
+ if (transition_latency) {
do_gettimeofday(&tv2);
+ local_irq_restore(flags);
+ }
*high_speed = speedstep_get_frequency(processor);
if (!*high_speed) {
@@ -464,8 +465,6 @@ unsigned int speedstep_get_freqs(enum sp
}
out:
- local_irq_restore(flags);
- preempt_enable();
return ret;
}
Index: linux-3.4.75/drivers/cpufreq/speedstep-smi.c
===================================================================
--- linux-3.4.75.orig/drivers/cpufreq/speedstep-smi.c 2014-01-16 18:51:16.000000000 +0100
+++ linux-3.4.75/drivers/cpufreq/speedstep-smi.c 2014-01-16 18:51:22.000000000 +0100
@@ -180,16 +180,16 @@ static int speedstep_get_state(void)
static void speedstep_set_state(unsigned int state)
{
unsigned int result = 0, command, new_state, dummy;
- unsigned long flags;
unsigned int function = SET_SPEEDSTEP_STATE;
unsigned int retry = 0;
if (state > 0x1)
return;
- /* Disable IRQs */
+ WARN_ON_ONCE(irqs_disabled());
+
+ /* Disable preemption so that other processes don't run */
preempt_disable();
- local_irq_save(flags);
command = (smi_sig & 0xffffff00) | (smi_cmd & 0xff);
@@ -209,9 +209,7 @@ static void speedstep_set_state(unsigned
*/
pr_debug("retry %u, previous result %u, waiting...\n",
retry, result);
- local_irq_enable();
mdelay(retry * 50);
- local_irq_disable();
}
retry++;
__asm__ __volatile__(
@@ -226,8 +224,7 @@ static void speedstep_set_state(unsigned
);
} while ((new_state != state) && (retry <= SMI_TRIES));
- /* enable IRQs */
- local_irq_restore(flags);
+ /* enable preemption */
preempt_enable();
if (new_state == state)
--
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