linux-kernel - Re: [PATCH 2/6] Add IRQ_TIME_ACCOUNTING, finer accounting of CPU irq time

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Date:	Mon, 20 Sep 2010 19:26:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 2/6] Add IRQ_TIME_ACCOUNTING, finer accounting of CPU
 irq time

On Mon, 2010-09-20 at 10:16 -0700, Venkatesh Pallipadi wrote:
> >> > You still do have the problem with local_bh_disable() though, since you
> >> > cannot distinguish between having bh disabled and processing softirq.
> >> >
> >> > So a hardirq that hits while you have bh disabled will inflate your
> >> > softirq time.

> >> Hmm, that bug is valid for CONFIG_VIRT_CPU_ACCOUNTING=y as well.
> >
> > And nobody ever noticed?
> >
> 
> Yes. I inherited the API from VIRT_CPU_ACCOUNTING along with this
> local_bh_disable bug. Agree that we need one extra bit to handle this
> case. I will take a stab at fixing this along with refresh of this
> patchset if no one else has beaten me to it until then. 

Make sure to only fix the softirq processing on the hardirq tail, not
the ksoftirqd one :-)
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