Message-Id: <200207111916.PAA08197@mc.com>
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From: mbs <mbs@mc.com>
To: george anzinger <george@mvista.com>, dank@kegel.com
Subject: Re: Periodic clock tick considered harmful (was: Re: HZ, preferably as  small as possible)
Date: Thu, 11 Jul 2002 15:19:01 -0400
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <3D2DB5F3.3C0EF4A2@kegel.com> <3D2DD734.5A3CA6EB@mvista.com>
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george, 

	with the HRT is there any reason to have 10 timer interrupts per process 
quantum anymore? (10 ms ticks, 100 ms proc quantum)


On Thursday 11 July 2002 15:06, george anzinger wrote:
> Ah, but you haven't looked at all that happens on a 1/HZ
> tick.  The high-res-timers patch does NOT eliminate the 1/HZ
> tick.  That tick is used to do a LOT of accounting activity
> which IMHO is best done by a periodic tick.  In particular,
> the time slice and execution time management depend on the
> periodic tick.  As a test we put together a tickless system,
> much as suggested above, and put enough stuff in it to see
> what the overhead was and how it changed.  The conclusion
> was that the timer over head increased far beyond the
> current overhead as soon as the system load (actually the
> number of context switches per second) increased beyond what
> a moderately busy system experiences.  In other words, the
> system was overload prone.  The current accounting activity
> is flat WRT to context switching which is IMHO just what it
> should be.  For those who want to know, a patch to put that
> test system together is still on the HRT sourceforge site.
>
> -g
>
> > OK, so I'm just an ignorant member of the peanut gallery, but
> > I'd like to hear a real kernel hacker explain why this isn't
> > the way to go.
> >
> > - Dan

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