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Date: Fri, 17 Jan 2014 02:21:18 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Mikulas Patocka <mpatocka@...hat.com>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
cpufreq@...r.kernel.org
Subject: Re: [PATCH] speedstep: clean up interrupt disabling (was: linux-next: build failure after merge of the tip tree)
On Thursday, January 16, 2014 02:33:02 PM Mikulas Patocka wrote:
>
> 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.
Well, I really don't appreciate sending me stuff like this two days before a
merge window. So I've dropped the speedstep_smi patch and please send me
something I can queue up for 3.15 without making Peter shudder.
Thanks!
> From: Mikulas Patocka <mpatocka@...hat.com>
> 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@...hat.com>
>
> ---
> 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)
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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