On Fri, 02 Oct 2009 11:25:10 -0700 Kok, Auke wrote: > Randy Dunlap wrote: > > Hi, > > > > I was looking into making mod_timer() be somewhat imprecise in when > > it sets the target timer to fire. The goal of this is saving power, > > as measured indirectly by powertop wakeups per second. > > > > There is already a notion of slack (or delta) time in > > kernel/hrtimer.c::hrtimer_start_range_ns() and in > > kernel/hrtimer.c::schedule_hrtimeout_range(), so maybe I'm attempting > > to modify the incorrect function, or maybe another interface function > > is needed for this. (?) > > > > I did find one user of hrtimer_start_range_ns() (in fs/ubifs/io.c). > > Is that the preferred interface to use when imprecise timers are > > acceptable? > > > > > > Results of this patch (that is below) are inconclusive IMO. > > I ran multiple runs of a short database test on an HP ProLiant BladeCenter > > (BL685c G1), which also has firmware for power usage measurements. > > > > averages: > > kernel 2.6.31 unpatched: 159 Watts, 302.7 wakeups/second > > kernel 2.6.31 + patch(N=9): 161 Watts, 291.1 wakeups/second > > kernel 2.6.31 + patch(N=19): 163 Watts, 316.3 wakeups/second > > kernel 2.6.31 + patch(N=99): 161 Watts, 284 wakeups/second > > > > > > Any comments or suggestions? > > > from the numbers you posted, I don't think you have a statistical significant > difference either way...
Yes. > but, more importantly, I wonder if the N numbers you are trying to delay > timers > are not too short in order for the system to actually draw much less power. > IOW > given your random load, C-state tables you might not expect to see that much > at all. OK, more testing with larger values of N: kernel 2.6.31 + patch(N=499): 160 Watts, 284.7 wakeups/second kernel 2.6.31 + patch(N=999): 147 Watts, 61.8 wakeups/second BUT test run takes 132 minutes instead of the usual 22 minutes!!! --- ~Randy [added Arjan to cc: list; he was supposed to be on it earlier] _______________________________________________ Discuss mailing list Discuss@lesswatts.org http://lists.lesswatts.org/listinfo/discuss
