Re: [PATCH v2] sched/cputime: add steal time support to full dynticks CPU time accounting

[Mika Penttilä]

On 05/18/2016 11:28 AM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng...@hotmail.com>
> 
> This patch adds steal guest time support to full dynticks CPU 
> time accounting. After 'commit ff9a9b4c4334 ("sched, time: Switch 
> VIRT_CPU_ACCOUNTING_GEN to jiffy granularity")', time is jiffy 
> based sampling even if it's still listened to ring boundaries, so 
> steal_account_process_tick() is reused to account how much 'ticks' 
> are steal time after the last accumulation. 
> 
> Suggested-by: Rik van Riel <r...@redhat.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Peter Zijlstra (Intel) <pet...@infradead.org>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Radim <rkrc...@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
> ---
> v1 -> v2:
>  * fix divide zero bug, thanks Rik
> 
>  kernel/sched/cputime.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 75f98c5..bfa50a0 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -257,7 +257,7 @@ void account_idle_time(cputime_t cputime)
>               cpustat[CPUTIME_IDLE] += (__force u64) cputime;
>  }
>  
> -static __always_inline bool steal_account_process_tick(void)
> +static __always_inline unsigned long steal_account_process_tick(void)
>  {
>  #ifdef CONFIG_PARAVIRT
>       if (static_key_false(&paravirt_steal_enabled)) {
> @@ -279,7 +279,7 @@ static __always_inline bool 
> steal_account_process_tick(void)
>               return steal_jiffies;
>       }
>  #endif
> -     return false;
> +     return 0;
>  }
>  
>  /*
> @@ -691,8 +691,12 @@ static cputime_t get_vtime_delta(struct task_struct *tsk)
>  
>  static void __vtime_account_system(struct task_struct *tsk)
>  {
> +     unsigned long steal_time = steal_account_process_tick();
>       cputime_t delta_cpu = get_vtime_delta(tsk);
>  
> +     if (steal_time >= delta_cpu)
> +             return;
> +     delta_cpu -= steal_time;
>       account_system_time(tsk, irq_count(), delta_cpu, 
> cputime_to_scaled(delta_cpu));
>  }
>  
> @@ -723,7 +727,12 @@ void vtime_account_user(struct task_struct *tsk)
>       write_seqcount_begin(&tsk->vtime_seqcount);
>       tsk->vtime_snap_whence = VTIME_SYS;
>       if (vtime_delta(tsk)) {
> +             unsigned long steal_time = steal_account_process_tick();
>               delta_cpu = get_vtime_delta(tsk);


afaik steal_account_process_tick() returns jiffies and get_vtime_delta() 
cputime, so can't mix them like this : ?

> +
> +             if (steal_time >= delta_cpu)
> +                     return;



> +             delta_cpu -= steal_time;
>               account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
>       }
>       write_seqcount_end(&tsk->vtime_seqcount);
> 


--Mika