linux-kernel - Re: [PATCH 6/6] Account ksoftirqd time as cpustat softirq -v1

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Message-ID: <1288085632.15336.111.camel@twins>
Date:	Tue, 26 Oct 2010 11:33:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Shaun Ruffell <sruffell@...ium.com>,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH 6/6] Account ksoftirqd time as cpustat softirq -v1

On Mon, 2010-10-25 at 15:30 -0700, Venkatesh Pallipadi wrote:
> softirq time in ksoftirqd context is not accounted in ns granularity
> per cpu softirq stats, as we want that to be a part of ksoftirqd
> exec_runtime.
> 
> Accounting them as softirq on /proc/stat separately.
> 
> Tested-by: Shaun Ruffell <sruffell@...ium.com>
> 
> Signed-off-by: Venkatesh Pallipadi <venki@...gle.com>
> ---
>  kernel/sched.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 49f6f61..0955050 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3617,6 +3617,14 @@ static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
>  		cpustat->irq = cputime64_add(cpustat->irq, tmp);
>  	} else if (irqtime_account_si_update()) {
>  		cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
> +	} else if (this_cpu_ksoftirqd() == p) {
> +		/*
> +		 * ksoftirqd time do not get accounted in cpu_softirq_time.
> +		 * So, we have to handle it separately here.
> +		 * Also, p->stime needs to be updated for ksoftirqd.
> +		 */
> +		__account_system_time(p, cputime_one_jiffy, one_jiffy_scaled,
> +					&cpustat->softirq);
>  	} else if (user_tick) {
>  		account_user_time(p, cputime_one_jiffy, one_jiffy_scaled);
>  	} else if (p == rq->idle) {


I'm somewhat confused by this patch.. This is significantly different
from the thing proposed last time around, which was to use:

  cpustat->softirq + this_cpu_ksoftirqd()->se.sum_exec_runtime

The above looses the fine grained aspect of the accounting and simply
charges a whole jiffy if the current process happens to be ksoftirqd.


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