Re: Network Stack Locking

From: Robert Watson (rwatson_at_FreeBSD.org)
Date: 05/25/04

  • Next message: Alan Cox: "Re: Network Stack Locking" 
    Date: Mon, 24 May 2004 23:49:11 -0400 (EDT)
To: Matthew Dillon <dillon@apollo.backplane.com>

    On Mon, 24 May 2004, Matthew Dillon wrote:

    > Deep message queues aren't necessarily a problem and, in fact, having
    > one or two dozen messages backed up in a protocol thread's message
    > port is actually good because the thread can then process all the
    > messages in a tight loop (cpu and cache locality of reference). If
    > designed properly, this directly mitigates the cost of a thread switch
    > as system load increases. So message queueing has the opposite effect...
    > per-unit handling overhead *decreases* as system load increases.

    Actually, this was the specific point I was making also :-). The question
    I was asking was about the depth of the message queues between protocol
    stack layers in actual measurements -- are you observing substantial
    coallescing between layers as a result of the queues at this point? I'm
    looking for emperical evidence that the coallescing does make up for the
    extra context switches of the model in practice...

    Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
    robert@fledge.watson.org Senior Research Scientist, McAfee Research

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