linux-kernel - Re: [PATCH 1/6] Free up pf flag PF

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Date:	Thu, 21 Oct 2010 10:13:51 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Venkatesh Pallipadi <venki@...gle.com>
cc:	Peter Zijlstra <peterz@...radead.org>, 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 1/6] Free up pf flag PF_KSOFTIRQD

On Wed, 20 Oct 2010, Venkatesh Pallipadi wrote:

> diff --git a/kernel/sched.c b/kernel/sched.c
> index abf8440..5d4afe9 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1984,9 +1984,9 @@ void account_system_vtime(struct task_struct *curr)
>  	 * in that case, so as not to confuse scheduler with a special task
>  	 * that do not consume any time, but still wants to run.
>  	 */
> -	if (hardirq_count())
> +	if (in_irq())
>  		per_cpu(cpu_hardirq_time, cpu) += delta;

If cpu is always the current cpu then you can optimize the code:

	this_cpu_add(cpu_hardirq_time, delta)

> -	else if (in_serving_softirq() && !(curr->flags & PF_KSOFTIRQD))
> +	else if (in_serving_softirq() && !(is_ksoftirqd_context()))
>  		per_cpu(cpu_softirq_time, cpu) += delta;

Same here.

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