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

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Date:	Wed, 18 May 2016 12:46:25 +0300
From:	Mika Penttilä <mika.penttila@...tfour.com>
To:	Wanpeng Li <kernellwp@...il.com>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>
CC:	Wanpeng Li <wanpeng.li@...mail.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paolo Bonzini <pbonzini@...hat.com>, Radim <rkrcmar@...hat.com>
Subject: Re: [PATCH v2] sched/cputime: add steal time support to full dynticks
 CPU time accounting

On 05/18/2016 11:28 AM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.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 <riel@...hat.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.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