Re: Network Stack Locking

From: Eivind Eklund (eivind_at_FreeBSD.org)
Date: 05/24/04

  • Next message: John Baldwin: "Re: '-h'/'-H' functionality." 
    Date: Mon, 24 May 2004 16:28:02 +0000
To: Robert Watson <rwatson@FreeBSD.org>

    On Fri, May 21, 2004 at 01:23:51PM -0400, Robert Watson wrote:
    > The other concern I have is whether the message queues get deep or not:
    > many of the benefits of message queues come when the queues allow
    > coallescing of context switches to process multiple packets. If you're
    > paying a context switch per packet passing through the stack each time you
    > cross a boundary, there's a non-trivial operational cost to that.

    I don't know what Matt has done here, but at least with the design we
    used for G2 (a private DFly-like project that John Dyson, I, and a few
    other people I don't know if want to be anonymous or not ran), this
    should not an issue. We used thread context passing with an API that
    contained putmsg_and_terminate() and message ports that automatically
    could spawn new handler threads. Effectively, a message-related context
    switch turned into "assemble everything I care about in a small package,
    reset the stack pointer, and go". The expectation was that this should
    end up with less overhead than function calls, as we could drop the call
    frames for "higher levels in the chain". We never got to the point
    where we could measure if it worked out that way in practice, though.

    Eivind.
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