Re: tcp_isn_tick() / dummynet() callout madness ?
From: Poul-Henning Kamp (phk_at_phk.freebsd.dk)
Date: 01/31/05
- Previous message: M. Warner Losh: "Re: [current tinderbox] failure on sparc64/sparc64"
- Maybe in reply to: Poul-Henning Kamp: "tcp_isn_tick() / dummynet() callout madness ?"
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To: Mike Silbersack <silby@silby.com> Date: Mon, 31 Jan 2005 08:56:44 +0100
In message <20050131011241.F64157@odysseus.silby.com>, Mike Silbersack writes:
>That sounds neat, but I'm not sure it's a good idea. In the case of tcp
>timers, there are multiple locks that are relevant, if I'm not mistaken.
>I also have this feeling that when mutex contention really matters, under
>serious load, it wouldn't be a good idea to indefinitely delay some
>callouts.
It is a good idea, if nothing else because it prevents us from stalling
softclock on a mutex we cannot get (for a long time).
>I'd propose a simpler approach: Two callout wheels. A "fast" callout
>wheel for short callouts (like tcp_isn_tick), and a "slow" callout wheel,
>for things like tcp timers which we should handle quickly, but won't care
>too much if they get delayed.
That is a worse idea because it almost doubles the overhead.
>Scott, in your reply to this you mention the importance of callouts firing
>on time - do we have such important callouts? Thinking from a system
>resource perspective, are there callouts that free memory, garbage
>collect, etc? It would make sense to give those priority over less
>critical timers which might block.
Yes, timeout firing precision is important.
-- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"
- Previous message: M. Warner Losh: "Re: [current tinderbox] failure on sparc64/sparc64"
- Maybe in reply to: Poul-Henning Kamp: "tcp_isn_tick() / dummynet() callout madness ?"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
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