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List:       freebsd-hackers
Subject:    Re: Clock Granularity (kernel option HZ)
From:       "Michael Meltzer" <mjm () michaelmeltzer ! com>
Date:       2002-01-31 23:34:55
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Not knowing but wondering:
With Gigabit Ethernet and NFS in the mix, anything that gets latency out is
a very good thing :-) and would improve performance.

MJM


----- Original Message -----
From: "Mike Silbersack" <silby@silby.com>
To: "Storms of Perfection" <gary@outloud.org>
Cc: <thierry@herbelot.com>; <replicator@ngs.ru>; <hackers@FreeBSD.ORG>
Sent: Thursday, January 31, 2002 12:33 PM
Subject: Re: Clock Granularity (kernel option HZ)


>
> On Thu, 31 Jan 2002, Storms of Perfection wrote:
>
> > I'm going to benchmark different network senarious with different
options
> > to see what I can get, and what works best. If someone wants to help me
> > out,  I could maybe write up a article about it?
>
> I don't think you'll end up seeing the performance improvements you're
> looking for.  The case where HZ=1000 is really useful is when using
> dummynet; the more accurate scheduling is necessary for it to handle high
> data rate pipes properly.
>
> The TCP stack, on the other hand, is perfectly happy with 10ms resolution.
> Retransmission timeouts are only actually used when loss occurs on the
> network, and 10ms is more than accurate enough for retransmission.  (I
> believe that retransmit timeouts are rounded up to 1 second, but don't
> quote me on that.)  The other timed events (keepalive timeouts, delayed
> ack timeouts, etc) are also in good shape with 10ms accuracy.
>
> So, it's highly unlikely that you'll be able to observe a perceptable
> difference in network performance except in really convoluted cases.
>
> Mike "Silby" Silbersack
>
>
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