Re: Periodic clock tick considered harmful (was: Re: HZ, preferably as small as possible)

["Per Jessen" <per@computer.org>]

On Thu, 11 Jul 2002 09:44:35 -0700, dank@kegel.com wrote:

>Mark Mielke <mark@mark.mielke.cc> wrote:
>> 
>> On Wed, Jul 10, 2002 at 04:09:21PM -0600, Cort Dougan wrote:
>> > Yes, please do make it a config option.  10x interrupt overhead makes me
>> > worry.  It lets users tailor the kernel to their expected load.
>> 
>> All this talk is getting to me.
>> 
>> I thought we recently (1 month ago? 2 months ago?) concluded that
>> increases in interrupt frequency only affects performance by a very
>> small amount, but generates an increase in responsiveness. The only
>> real argument against that I have seen, is the 'power conservation'
>> argument. The idea was, that the scheduler itself did not execute
>> on most interrupts. The clock is updated, and that is about all.
>
>On UML and mainframe Linux, *any* periodic clock tick 
>is heavy overhead when you have a large number of 
>(mostly idle) instances of Linux running, isn't it?   

Without knowing what UML is in this context, but assuming that mainframe
means IBM s390 mainframes, I can confirm that any periodic clock tick
is heavy overhead. With or without (mostly) idle instances. 

/Per



regards,
Per Jessen, Zurich
http://www.enidan.com - home of the J1 serial console.

Windows 2001: "I'm sorry Dave ...  I'm afraid I can't do that."