linux-kernel - Re: [PATCH 2/3] smp: re-implement the kick_all_cpus_sync() with wake_up_if

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Date:	Fri, 15 Aug 2014 08:40:53 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Liu, Changcheng" <changcheng.liu@...el.com>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>,
	"Chakravarty, Souvik K" <souvik.k.chakravarty@...el.com>
Subject: Re: [PATCH 2/3] smp: re-implement the kick_all_cpus_sync() with wake_up_if_idle()

On Fri, Aug 15, 2014 at 12:01 AM, Chuansheng Liu
<chuansheng.liu@...el.com> wrote:
> Currently using smp_call_function() just woke up the corresponding
> cpu, but can not break the polling idle loop.
>
> Here using the new sched API wake_up_if_idle() to implement it.

kick_all_cpus_sync has other callers, and those other callers want the
old behavior.  I think this should be a new function.

--Andy

>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
> ---
>  kernel/smp.c |   18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index aff8aa1..0b647c3 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -13,6 +13,7 @@
>  #include <linux/gfp.h>
>  #include <linux/smp.h>
>  #include <linux/cpu.h>
> +#include <linux/sched.h>
>
>  #include "smpboot.h"
>
> @@ -677,10 +678,6 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
>  }
>  EXPORT_SYMBOL(on_each_cpu_cond);
>
> -static void do_nothing(void *unused)
> -{
> -}
> -
>  /**
>   * kick_all_cpus_sync - Force all cpus out of idle
>   *
> @@ -694,8 +691,15 @@ static void do_nothing(void *unused)
>   */
>  void kick_all_cpus_sync(void)
>  {
> -       /* Make sure the change is visible before we kick the cpus */
> -       smp_mb();
> -       smp_call_function(do_nothing, NULL, 1);
> +       int cpu;
> +
> +       preempt_disable();
> +       for_each_online_cpu(cpu) {
> +               if (cpu == smp_processor_id())
> +                       continue;
> +
> +               wake_up_if_idle(cpu);
> +       }
> +       preempt_enable();
>  }
>  EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
> --
> 1.7.9.5
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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