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To: Andrew Gallatin <gallatin@cs.duke.edu>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Fri, 14 Oct 2005 15:19:19 EDT."
	<17232.1207.615226.432579@grasshopper.cs.duke.edu> 
Date: Fri, 14 Oct 2005 21:36:28 +0200
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Cc: Garrett Wollman <wollman@csail.mit.edu>, net@FreeBSD.org
Subject: Re: Call for performance evaluation: net.isr.direct (fwd) 
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In message <17232.1207.615226.432579@grasshopper.cs.duke.edu>, Andrew Gallatin 
writes:
>
>Poul-Henning Kamp writes:
> > The solution is not faster but less reliable timekeeping, the
> > solution is to move the scheduler(s) away from using time as an
> > approximation of cpu cycles.
>
>So you mean rather than use binuptime() in mi_switch(), use some
>per-cpu cycle counter (like rdtsc)?

yes.

>Heck, why not just use ticks for the scheduler and keep the expensive
>timekeeping code out of the critical path altogether?  Does it really
>need better than 1ms resolution?

Because the resource accounting needs to know how much cpu power
each process/thread has used, and the units used assume a constant
clockrate (see times(3))

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.