Re: [tip:timers/urgent] NOHZ: Properly feed cpufreq ondemand governor

Eero Nurkkala
2009-05-27T12:20:43Z

On Wed, 2009-05-27 at 13:57 +0200, Nurkkala Eero.An (EXT-Offcode/Oulu)
wrote:
> Commit-ID: 4e67ac87c460a3c876019fa05149591122ec5287
> Gitweb: http://git.kernel.org/tip/4e67ac87c460a3c876019fa05149591122ec5287
> Author: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
> AuthorDate: Mon, 25 May 2009 09:57:37 +0300
> Committer: Thomas Gleixner <tglx@linutronix.de>
> CommitDate: Wed, 27 May 2009 13:55:00 +0200
>
> NOHZ: Properly feed cpufreq ondemand governor
>
> A call from irq_exit() may occasionally pause the timing
> info for cpufreq ondemand governor. This results in the
> cpufreq ondemand governor to fail to calculate the
> system load properly. Thus, relocate the checks for this
> particular case to keep the governor always functional.
>
> [ tglx: moved the check to the top of the function ]
>
> Signed-off-by: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
> Reported-by: Tero Kristo <tero.kristo@nokia.com>
> Acked-by: Rik van Riel <riel@redhat.com>
> Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
> LKML-Reference: <12432346571351-git-send-email-ext-eero.nurkkala@nokia.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
>
> ---
> kernel/time/tick-sched.c | 12 ++++++++----
> 1 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index d3f1ef4..d3d6f3f 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -218,8 +218,15 @@ void tick_nohz_stop_sched_tick(int inidle)
> struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
> int cpu;
>
> - local_irq_save(flags);
> + /*
> + * Call to tick_nohz_start_idle stops the last_update_time from being
> + * updated. Thus, it must not be called in the event we are called from
> + * irq_exit() with the prior state different than idle.
> + */
> + if (!inidle && !ts->inidle)
> + return;
>
> + local_irq_save(flags);
> cpu = smp_processor_id();
> ts = &per_cpu(tick_cpu_sched, cpu);
> now = tick_nohz_start_idle(ts);
> @@ -239,9 +246,6 @@ void tick_nohz_stop_sched_tick(int inidle)
> if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
> goto end;
>
> - if (!inidle && !ts->inidle)
> - goto end;
> -
> ts->inidle = 1;
>
> if (need_resched())

A quick note:
Now ts is uninitialized? So ts->inidle could cause troubles, no?