linux-kernel - Re: System tick rate

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Date:	Mon, 16 Mar 2009 19:11:32 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: System tick rate


On Friday 2009-03-13 09:49, Peter Zijlstra wrote:
>On Thu, 2009-03-12 at 15:45 +0100, Jan Engelhardt wrote:
>> On Thursday 2009-03-12 15:21, Arjan van de Ven wrote:
>> >On Thu, 12 Mar 2009 14:38:19 +0100 (CET) Jan Engelhardt wrote:
>> >> 
>> >> is there an "official" way of obtaining the current tick rate when 
>> >> CONFIG_NO_HZ? 
>> >
>> >what does "current tick rate" mean for you in a no-hz situation ?
>> >is it the HZ value (which is supposed to be invisible from userspace,
>> >so good luck) or the wakeup count ?
>> 
>> Hm, I guess what I want is the number of timer interrupts which
>> occurred within the observation period that called the scheduler
>> code. (So that excludes RTC on usual x86en.)
>
>There is no tick rate with NO_HZ mode, only a max tick rate, but as
>Arjan said, not even that is exposed to user-space.
>
>I think Dave's Niagra has the crown here, because he ran into some bug
>in the NO_HZ code some while back because he idled longer than we ever
>seen before. I think it was in the order of 30 minutes or something
>without a single wakeup of the CPU.
>
Well if it idled that long, it surely did not run any processes, did it?
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