Messages in this thread Patch in this message | | | Date | Fri, 8 Feb 2008 09:24:30 -0800 | From | Venki Pallipadi <> | Subject | Re: [PATCH] x86: Simplify cpu_idle_wait |
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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
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@intel.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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