Re: Variable timer tick rate?

From: Bruce Evans (bde_at_zeta.org.au)
Date: 10/19/03

  • Next message: Poul-Henning Kamp: "Re: DISCUSSION: /dev/fd%d.%d and /dev/{a}cd%d[ac] to be discontinued ?" 
    Date: Sun, 19 Oct 2003 09:23:51 +1000 (EST)
To: Poul-Henning Kamp <phk@phk.freebsd.dk>

    On Sat, 18 Oct 2003, Poul-Henning Kamp wrote:

    > In message <20031018130119.T47207@root.org>, Nate Lawson writes:
    >
    > >This is an interesting approach. If there are no upcoming timeouts,
    > >decrease the tick rate. Of course, you have to amortize the cost of
    > >resetting the timer over the period of no ticks.
    > >
    > >http://kerneltrap.org/node/view/1006

    Doing this to increase (instead of decrease) the tick rate is an old
    topic. I think it would have too high an overhead (at least for the
    increase case, at least on i386's), since reprogramming the i8254
    timer takes a few usec. A few usec every 1/HZ for the default HZ
    wouldn't be too bad.

    > Yes, unfortunately we may have a couple of timeout() (ab)users which
    > use it to implement "as fast as possible polling" by calling timeout
    > with a 1 tick argument, so last I looked (a couple of years ago)
    > it fired every tick.

    Also, some things like to increase HZ to 1000 or more to poll faster,
    so even the timeout users that don't know better than to use a timeout
    of 1 tick get faster polling.

    Bruce
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