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Date:      Wed, 18 Apr 2001 02:21:04 +0000 (GMT)
From:      "E.B. Dreger" <eddy+public+spam@noc.everquick.net>
To:        Matt Dillon <dillon@earth.backplane.com>
Cc:        Alfred Perlstein <bright@wintelcom.net>, Greg Lehey <grog@lemis.com>, "Justin T. Gibbs" <gibbs@scsiguy.com>, Doug Barton <DougB@DougBarton.net>, "current @ freebsd . org" <current@FreeBSD.ORG>
Subject:   Re: Kernel preemption, yes or no? (was: Filesystem gets a huge performance boost)
Message-ID:  <Pine.LNX.4.20.0104180211450.14449-100000@www.everquick.net>
In-Reply-To: <200104180206.f3I268716829@earth.backplane.com>

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> Date: Tue, 17 Apr 2001 19:06:08 -0700 (PDT)
> From: Matt Dillon <dillon@earth.backplane.com>
> 
> They don't have to be.  If you have four NICs each one can be its own
> interrupt, each with its own mutex.  Thus all four can be taken in
> parallel.  I was under the impression that BSDI had achieved that
> in their scheme.

IIRC, didn't the NT driver for some NIC (Intel?) switch to polling,
anyway, under heavy load?  The reasoning being that you _know_ that you're
going to get something... why bother an IRQ hit?

That said, IRQ distribution sounds like a good thing for the general case.

> If you have one NIC then obviously you can't take multiple interrupts
> for that one NIC on different cpu's.  No great loss, you generally don't
> want to do that anyway.

Actually, I should think that one would _want_ to serialize traffic for a
given NIC.  (I'm ignoring when one trunks NICs... speaking of which,
anyone have info on 802.3ad? ;-)  Otherwise, one ends up with a race that
[potentially] screws up packet sequence.


Eddy

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