Date: Sun, 19 Oct 2003 09:23:51 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: Nate Lawson <nate@root.org> Subject: Re: Variable timer tick rate? Message-ID: <20031019091024.O2998@gamplex.bde.org> In-Reply-To: <9670.1066507540@critter.freebsd.dk> References: <9670.1066507540@critter.freebsd.dk>
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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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