[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 0/2] range timer support
2008/10/30 Keir Fraser <keir.fraser@xxxxxxxxxxxxx>: > On 30/10/08 08:08, "Yu, Ke" <ke.yu@xxxxxxxxx> wrote: > >>> Increasing SLOP to 1ms should have the the similar 5% gain, as your >>> analysis, it is the worst case of range timer application in vpt. I >>> can redo the measurement to double confirm. >> >> I have finished the measurement, when TIME_SLOP increase to 1ms, there is >> similar power consumption gain, this time it is 4% (14.0W vs 14.6W) . By >> theory 1ms TIMER_SLOP should have more gain than the range timer. The >> diferrence may be due to the test environment noise. > > It may also be because your patch tends to delay the timer deadline > somewhat, and so by the time it goes off you actually sometimes have one or > two more timers you can deliver in the batch? OTOH it could be experimental > noise as you suggest, and certainly this change gets us pretty close to your > win. We'd have to do further experiments to see if increasing TIMER_SLOP > noticeably degrades system performance, but we'd need to do that with the > range-timer approach too. oh yes, you remind me that the range timer also has 50ns TIMER_SLOP, this may also help. and yes, I am doing the range timer performance test, to make sure it does not hurt performance. I can also test the performance of 1ms TIMER_SLOP. > > One thing: as Dan pointed out, some things don't want to get their timeout > early, but generally callers are much more tolerant of getting timeouts a > bit late. Possibly we should set the timer_deadline to nearest timeout + > TIMER_SLOP, and then when executing timers be strict about not executing > timers early (or at least no more than the existing 50us 'mini' slop)? yes, this way can avoid the issue Dan pointed out. > > Or perhaps actually having range timers in timer.c is worthwhile for future > extensions and for now we can just set every timer to [deadline, > deadline+configurable_global_slop]. Then the existing range-timer mechanism > ought to find a sensible deadline to aim for, only delaying timer events > when there is a benefit to doing so. I am fine with configurable global slop, although some timer may not benefit much from this. e.g. the 50HZ (20ms) cpufreq DBS timer, whose timer range can be at least [deadline, deadline+5ms] :) Best Regards Ke > > I'm thinking out loud. :-) > > -- Keir > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |