Messages in this thread | | | From | David Brownell <> | Subject | Re: [PATCH] suppress needless timer reprogramming {tick-sched.c} | Date | Wed, 18 Jun 2008 09:28:41 -0700 |
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On Wednesday 18 June 2008, Woodruff, Richard wrote: > > > > As measured using ETM trace this drops my reprogramming penalty from > > almost 60% CPU load down to 15% during high interrupt rate. If you like > > I can send traces to show this.
More than doubling the available-for-real-use CPU time! Impressive.
I'd imagine that many systems using reprogrammable 32K timers for scheduling could win from such a patch, although not necessarily quite so visibly as on this ARM unless their CPU clocks were also in the 500+ MHz range.
Seems like a "law of unintended consequences" here. Use a 32K timer since it takes less power than a multi-MHz one, and so the faster clocks can be gated off more comprehensively (in hardware) to give more power savings. Then throw NO_HZ on top to get one more increment of power savings ... whoops, it was assuming that it was dirt cheap to reprogram timers, major badness!
- Dave
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