linux-kernel - Re: [PATCH 2/3] sched/cputime: code cleanup in irqtime_account_process

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Date:   Mon, 6 Jan 2020 16:53:51 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] sched/cputime: code cleanup in
 irqtime_account_process_tick

On Thu, Jan 02, 2020 at 06:07:53PM +0800, Alex Shi wrote:
> In this func, since account_system_time() considers guest time account
> and other system time.  we could fold the account_guest_time into
> account_system_time() to simply the code.
> 
> Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Wanpeng Li <wanpeng.li@...mail.com>
> Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-kernel@...r.kernel.org
> ---
>  kernel/sched/cputime.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index cff3e656566d..46b837e94fce 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -381,13 +381,10 @@ static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
>  		account_system_index_time(p, cputime, CPUTIME_SOFTIRQ);
>  	} else if (user_tick) {
>  		account_user_time(p, cputime);
> -	} else if (p == this_rq()->idle) {
> +	} else if ((p != this_rq()->idle) || (irq_count() != HARDIRQ_OFFSET))
> +		account_system_time(p, HARDIRQ_OFFSET, cputime);
> +	else

I fear we can't really play the exact same game as account_process_tick() here.
Since this is irqtime precise accounting, we have already computed the
irqtime delta in account_other_time() (or we will at some point in the future)
and substracted it from the ticks to account. This means that the remaining cputime
to account has to be either utime/stime/gtime/idle-time but not interrupt time, or
we may account interrupt time twice. And account_system_time() tries to account
irq time, for example if we interrupt a softirq.

Thanks.


>  		account_idle_time(cputime);
> -	} else if (p->flags & PF_VCPU) { /* System time or guest time */
> -		account_guest_time(p, cputime);
> -	} else {
> -		account_system_index_time(p, cputime, CPUTIME_SYSTEM);
> -	}
>  }
>  
>  static void irqtime_account_idle_ticks(int ticks)
> -- 
> 1.8.3.1
>