From owner-freebsd-current  Tue Apr 17 19:35: 1 2001
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Date: Tue, 17 Apr 2001 19:34:56 -0700 (PDT)
From: Matt Dillon <dillon@earth.backplane.com>
Message-Id: <200104180234.f3I2Yuq17047@earth.backplane.com>
To: "E.B. Dreger" <eddy+public+spam@noc.everquick.net>
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)
References:  <Pine.LNX.4.20.0104180211450.14449-100000@www.everquick.net>
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: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.

    Under a full load polling would work just as well as an interrupt.
    With NT for the network tests they hardwired each NIC to a particular
    CPU.  I don't know if they did any polling or not.

:> 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

    Yes.  Also NICs usually have circular buffers for packets so, really,
    only one cpu can be processing a particular NIC's packets at any given
    moment.

					-Matt

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