On Tue, 2008-09-16 at 14:42 +0530, Arun R Bharadwaj wrote: > Hi, 80 char lines please. > An idle cpu on which device drivers have initialized timers, has to be > frequently woken up to service the timers. So, consolidation of timers > onto a fewer number of cpus is important. Migration of > timers from idle cpus onto lesser idle cpus is necessary. Currently, > timers are migrated during the cpu offline operation. However > cpu-hotplug for the sake of idle system power management is too > heavy. So, this patch implements a lightweight timer migration > framework. > > Also, in a multi-core, multi-package system, it is always desirable to > have all the timers firing on the cpus present in the same package. > This would enable us to place the idle package in deep sleep > state. So, migration of timers is required for this. > > A per_cpu sysfs hook is created > at /sys/devices/system/cpu/cpuX/timer_migration. By echo-ing 1 to > cpuX/timer_migration, all regular and hrtimers from cpuX are migrated > to cpu0. The fact that all > timers are migrated from cpuX to cpu0 is demonstrated by making a note > of /proc/interrupts. This seems like an exceedingly dumb idea - cpu 0 might be a long long way from x and by pushing all timers to cpu0 you might actually overload cpu 0. Initially you talked about packages an moving timers to busy cpus - which is something else altogether. > $:echo 1 > /sys/devices/system/cpu/cpu3/timer_migration > $:cat /proc/interrupts > file1; sleep 30 ; cat /proc/interrupts > > file2 > $:diff file1 file2 | grep LOC > < LOC: 5276 2100 2676 1647 2415 > 1803 2275 2977 Local timer interrupts > > LOC: 6991 2195 2774 1647 2562 > 1900 2497 3075 Local timer interrupts > > As we can observe, first we are enabling timer migration in cpu3. As a > result, the number of local timer interrupts on cpu3 over the next 30 > seconds are zero. cpu3 has been totally rid of all regular > and hrtimers. > > Please refer to the following paper for details: > > http://ols.fedoraproject.org/OLS/Reprints-2008/srinivasan1-reprint.pdf If there's anything worth reading in there it should have been mentioned in this email and preferably in some comment in the code and Kconfig help as well. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
