Re: [PATCH v6 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting

[Paolo Bonzini]

On 13/06/2016 12:32, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> 
> This patch adds guest steal-time support to full dynticks CPU
> time accounting. After the following commit:
> 
> ff9a9b4c4334 ("sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity")
> 
> ... time sampling became jiffy based, even if it's still listening to ring
>  boundaries, so steal_account_process_tick() is reused to account how many
> 'ticks' are stolen-time, after the last accumulation.
> 
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
>  kernel/sched/cputime.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 75f98c5..3d60e5d 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(unsigned long max_jiffies)
>  {
>  #ifdef CONFIG_PARAVIRT
>  	if (static_key_false(&paravirt_steal_enabled)) {
> @@ -272,14 +272,14 @@ static __always_inline bool steal_account_process_tick(void)
>  		 * time in jiffies. Lets cast the result to jiffies
>  		 * granularity and account the rest on the next rounds.
>  		 */
> -		steal_jiffies = nsecs_to_jiffies(steal);
> +		steal_jiffies = min(nsecs_to_jiffies(steal), max_jiffies);
>  		this_rq()->prev_steal_time += jiffies_to_nsecs(steal_jiffies);
>  
>  		account_steal_time(jiffies_to_cputime(steal_jiffies));
>  		return steal_jiffies;
>  	}
>  #endif
> -	return false;
> +	return 0;
>  }
>  
>  /*
> @@ -346,7 +346,7 @@ static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
>  	u64 cputime = (__force u64) cputime_one_jiffy;
>  	u64 *cpustat = kcpustat_this_cpu->cpustat;
>  
> -	if (steal_account_process_tick())
> +	if (steal_account_process_tick(ULONG_MAX))
>  		return;
>  
>  	cputime *= ticks;
> @@ -477,7 +477,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
>  		return;
>  	}
>  
> -	if (steal_account_process_tick())
> +	if (steal_account_process_tick(ULONG_MAX))
>  		return;
>  
>  	if (user_tick)
> @@ -681,12 +681,14 @@ static cputime_t vtime_delta(struct task_struct *tsk)
>  static cputime_t get_vtime_delta(struct task_struct *tsk)
>  {
>  	unsigned long now = READ_ONCE(jiffies);
> -	unsigned long delta = now - tsk->vtime_snap;
> +	unsigned long delta_jiffies, steal_jiffies;
>  
> +	delta_jiffies = now - tsk->vtime_snap;
> +	steal_jiffies = steal_account_process_tick(delta_jiffies);
>  	WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_INACTIVE);
>  	tsk->vtime_snap = now;
>  
> -	return jiffies_to_cputime(delta);
> +	return jiffies_to_cputime(delta_jiffies - steal_jiffies);
>  }
>  
>  static void __vtime_account_system(struct task_struct *tsk)
> 

Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>