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Message-ID: <alpine.LFD.1.00.0802091029400.3145@apollo.tec.linutronix.de>
Date: Sat, 9 Feb 2008 10:33:21 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: Venki Pallipadi <venkatesh.pallipadi@...el.com>
cc: Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>,
"Brown, Len" <len.brown@...el.com>, Adam Belay <abelay@...ell.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Simplify cpu_idle_wait
On Fri, 8 Feb 2008, Venki Pallipadi wrote:
> On Fri, Feb 08, 2008 at 11:28:48AM +0100, Andi Kleen wrote:
> >
> > > - set_cpus_allowed(current, tmp);
> > > + smp_mb();
> > > + /* kick all the CPUs so that they exit out of pm_idle */
> > > + smp_call_function(do_nothing, NULL, 0, 0);
> >
> > I think the last argument (wait) needs to be 1 to make sure it is
> > synchronous (for 32/64) Otherwise the patch looks great.
>
> Yes. Below is the updated patch
Applied. Thanks,
tglx
> Earlier commit 40d6a146629b98d8e322b6f9332b182c7cbff3df
> added smp_call_function in cpu_idle_wait() to kick cpus that are in tickless
> idle. Looking at cpu_idle_wait code at that time, code seemed to be
> over-engineered for a case which is rarely used (while changing idle handler).
>
> Below is a simplified version of cpu_idle_wait, which just makes
> a dummy smp_call_function to all cpus, to make them come out of old idle handler
> and start using the new idle handler. It eliminates code in the idle loop
> to handle cpu_idle_wait.
>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
>
> Index: linux-2.6.25-rc/arch/x86/kernel/process_32.c
> ===================================================================
> --- linux-2.6.25-rc.orig/arch/x86/kernel/process_32.c
> +++ linux-2.6.25-rc/arch/x86/kernel/process_32.c
> @@ -82,7 +82,6 @@ unsigned long thread_saved_pc(struct tas
> */
> void (*pm_idle)(void);
> EXPORT_SYMBOL(pm_idle);
> -static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
>
> void disable_hlt(void)
> {
> @@ -181,9 +180,6 @@ void cpu_idle(void)
> while (!need_resched()) {
> void (*idle)(void);
>
> - if (__get_cpu_var(cpu_idle_state))
> - __get_cpu_var(cpu_idle_state) = 0;
> -
> check_pgt_cache();
> rmb();
> idle = pm_idle;
> @@ -208,40 +204,19 @@ static void do_nothing(void *unused)
> {
> }
>
> +/*
> + * cpu_idle_wait - Used to ensure that all the CPUs discard old value of
> + * pm_idle and update to new pm_idle value. Required while changing pm_idle
> + * handler on SMP systems.
> + *
> + * Caller must have changed pm_idle to the new value before the call. Old
> + * pm_idle value will not be used by any CPU after the return of this function.
> + */
> void cpu_idle_wait(void)
> {
> - unsigned int cpu, this_cpu = get_cpu();
> - cpumask_t map, tmp = current->cpus_allowed;
> -
> - set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
> - put_cpu();
> -
> - cpus_clear(map);
> - for_each_online_cpu(cpu) {
> - per_cpu(cpu_idle_state, cpu) = 1;
> - cpu_set(cpu, map);
> - }
> -
> - __get_cpu_var(cpu_idle_state) = 0;
> -
> - wmb();
> - do {
> - ssleep(1);
> - for_each_online_cpu(cpu) {
> - if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
> - cpu_clear(cpu, map);
> - }
> - cpus_and(map, map, cpu_online_map);
> - /*
> - * We waited 1 sec, if a CPU still did not call idle
> - * it may be because it is in idle and not waking up
> - * because it has nothing to do.
> - * Give all the remaining CPUS a kick.
> - */
> - smp_call_function_mask(map, do_nothing, 0, 0);
> - } while (!cpus_empty(map));
> -
> - set_cpus_allowed(current, tmp);
> + smp_mb();
> + /* kick all the CPUs so that they exit out of pm_idle */
> + smp_call_function(do_nothing, NULL, 0, 1);
> }
> EXPORT_SYMBOL_GPL(cpu_idle_wait);
>
> Index: linux-2.6.25-rc/arch/x86/kernel/process_64.c
> ===================================================================
> --- linux-2.6.25-rc.orig/arch/x86/kernel/process_64.c
> +++ linux-2.6.25-rc/arch/x86/kernel/process_64.c
> @@ -64,7 +64,6 @@ EXPORT_SYMBOL(boot_option_idle_override)
> */
> void (*pm_idle)(void);
> EXPORT_SYMBOL(pm_idle);
> -static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
>
> static ATOMIC_NOTIFIER_HEAD(idle_notifier);
>
> @@ -139,41 +138,19 @@ static void do_nothing(void *unused)
> {
> }
>
> +/*
> + * cpu_idle_wait - Used to ensure that all the CPUs discard old value of
> + * pm_idle and update to new pm_idle value. Required while changing pm_idle
> + * handler on SMP systems.
> + *
> + * Caller must have changed pm_idle to the new value before the call. Old
> + * pm_idle value will not be used by any CPU after the return of this function.
> + */
> void cpu_idle_wait(void)
> {
> - unsigned int cpu, this_cpu = get_cpu();
> - cpumask_t map, tmp = current->cpus_allowed;
> -
> - set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
> - put_cpu();
> -
> - cpus_clear(map);
> - for_each_online_cpu(cpu) {
> - per_cpu(cpu_idle_state, cpu) = 1;
> - cpu_set(cpu, map);
> - }
> -
> - __get_cpu_var(cpu_idle_state) = 0;
> -
> - wmb();
> - do {
> - ssleep(1);
> - for_each_online_cpu(cpu) {
> - if (cpu_isset(cpu, map) &&
> - !per_cpu(cpu_idle_state, cpu))
> - cpu_clear(cpu, map);
> - }
> - cpus_and(map, map, cpu_online_map);
> - /*
> - * We waited 1 sec, if a CPU still did not call idle
> - * it may be because it is in idle and not waking up
> - * because it has nothing to do.
> - * Give all the remaining CPUS a kick.
> - */
> - smp_call_function_mask(map, do_nothing, 0, 0);
> - } while (!cpus_empty(map));
> -
> - set_cpus_allowed(current, tmp);
> + smp_mb();
> + /* kick all the CPUs so that they exit out of pm_idle */
> + smp_call_function(do_nothing, NULL, 0, 1);
> }
> EXPORT_SYMBOL_GPL(cpu_idle_wait);
>
> @@ -215,9 +192,6 @@ void cpu_idle (void)
> while (!need_resched()) {
> void (*idle)(void);
>
> - if (__get_cpu_var(cpu_idle_state))
> - __get_cpu_var(cpu_idle_state) = 0;
> -
> tick_nohz_stop_sched_tick();
>
> rmb();
>
--
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