linux-kernel - Re: inaccurate cpu idle time from top command

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Message-ID: <2f495dc80907252034i4bdd812cx2267d65af7d993d8@mail.gmail.com>
Date:	Sun, 26 Jul 2009 11:34:02 +0800
From:	Fred Fan <fanyefeng@...il.com>
To:	cocala <syy.wxd@...il.com>
Cc:	linux-arm-kernel@...ts.arm.linux.org.uk, rick.jones2@...com,
	gallatin@...i.com, akpm@...ux-foundation.org, dada1@...mosbay.com,
	schwidefsky@...ibm.com, brice@...i.com, paulus@...ba.org,
	benh@...nel.crashing.org, mingo@...e.hu, gregkh@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: inaccurate cpu idle time from top command

Hi cocala:
    I have met same issue. And we found the total utilization
count(added by idle's utilization) is not 100% in detail processes
information fields.
   best Regards
Fred

2009/7/24 cocala <syy.wxd@...il.com>:
> I saw one commit "3209ada8285a9fa6ab8f7a731d54031ec884c745 - sched: account
> system time properly"
> This commit is to take into account timer IRQ interrupting the idle task
> servicing a hard or soft irq.
>
> If a softirq is started in a tick, all the time in the tick will be counted
> as soft irq time even most time in the tick is idle.
> In our use case, one jiffy is 10ms and the 1G net driver will generate many
> software irq, so the "top" command will show high softare irq time and cpu
> idle time approaches to zero.
> If I change the jiffy to 1ms, the "top" command shows much higher cpu idle
> time. I think this algorithm is also not fair for some cases.
>
> Is there any better way to count the softare irq time?
>
> Thanks
> cocala
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