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Message #00167
[Blueprint hrtimer-range-and-clockevent] misc: make possible to use the range field of hrtimer into the clockevent driver
Blueprint changed by Dmitry Antipov:
Whiteboard changed:
Hrtimer satisfies a wide range of requirements so optimizing it for powersaving can be an interesting task. Basically the clock event driver exposes the interface to schedule the actual next event interrupt. The time to schedule this interrupt is passed as a parameter by core timers interface after checking the other timers registered along with their ranges. This range field of Hrtimer is a important field in reducing the number of timers firing and thus less wakeus by merging the timers together.
http://lwn.net/Articles/299590
Some activity identified are,
* Use sleep_range api's instead of normal sleep in drivers and test
applications(check possibility). More such type of timers will help in
benchmarkings
* Use the range field of timers (Along with any synchronization needed)
in the clock event driver itself before scheduling the next event
interrupt.
* Benchmark and measure the C state idle wakeups and no of process wakeups.
A good way to test the benefit of adding a range parameter to the clock-event, is to check how this help to synchronize the wake-up/sleep sequence of the cores in the same cluster. The main benefit should be an increase on the cluster power down mode.
Let start on each core a thread, which uses hrtimer with range, to simulate periodic activity. The use a range in clock event should help to synchronize the wakeup of cores and to the improve the time spent in cluster off mode
Work items for 2012.01:
[dmitry.antipov] implement core high-res timers feature to return time spent in usleep_range(): DONE
[dmitry.antipov] adapt OMAP I2C driver to use this feature: DONE
[dmitry.antipov] adapt SMSC95XX driver to use this feature: DONE
[dmitry.antipov] convert MMC/SD host driver to usleep_range(): DONE
Work items for 2012.02:
[dmitry.antipov] Push mmc, omap_i2c and smsc95xx changes to mainline: INPROGRESS
[dmitry.antipov] Find and classify the kernel wide timers other then hrtimer subsystem which uses clock event driver to register the h/w timer: TODO
[dmitry.antipov] Implement a test case/benchmark to check whether high-res timers should be preferred over jiffies-backed timers in a different situations for a different kinds of workload: TODO
[dmitry.antipov] To create a preliminary design or even sample implementation of putting the range field in clock event driver: TODO
[dmitry.antipov] Get the above design reviewed before proceeding further: TODO
+
+ Benchmark results obtained with oprofile on Panda board:
+
+ There is a sample kernel module to create a lot of kernel threads, each
+ of them do schedule_timeout_uninterruptible() or
+ schedule_hrtimeout_range():
+
+ https://wiki.linaro.org/WorkingGroups/PowerManagement/Doc?action=AttachFile&do=view&target=timeoutbench.c
+
+ With default parameters (128 threads, 1 ms timeout) and jiffies-backed
+ timeout, vmlinux profiling gives the following results:
+
+ samples % samples % image name app name symbol name
+ 101123 96.9038 0 0 vmlinux vmlinux omap4_enter_idle
+ 825 0.7906 13 0.0124 vmlinux vmlinux tick_nohz_idle_enter
+ 726 0.6957 55 0.0526 vmlinux vmlinux __schedule
+ 86 0.0824 7 0.0067 vmlinux vmlinux lock_acquire
+ 77 0.0738 0 0 vmlinux vmlinux run_ksoftirqd
+ 67 0.0642 5 0.0048 vmlinux vmlinux sub_preempt_count
+ 63 0.0604 4 0.0038 vmlinux vmlinux tick_nohz_idle_exit
+ 61 0.0585 0 0 vmlinux vmlinux __do_softirq
+ 61 0.0585 3 0.0029 vmlinux vmlinux rcu_note_context_switch
+ 56 0.0537 1 9.6e-04 vmlinux vmlinux add_preempt_count
+
+ For high-resolution timers timeout, vmlinux profiling gives the
+ following:
+
+ samples % samples % image name app name symbol name
+ 5992 31.8013 0 0 vmlinux vmlinux omap4_enter_idle
+ 3594 19.0744 3793 2.1795 vmlinux vmlinux __schedule
+ 2917 15.4814 2804 1.6112 vmlinux vmlinux __hrtimer_start_range_ns
+ 1224 6.4961 1235 0.7096 vmlinux vmlinux hrtimer_try_to_cancel
+ 412 2.1866 483 0.2775 vmlinux vmlinux lock_acquire
+ 328 1.7408 281 0.1615 vmlinux vmlinux schedule_hrtimeout_range_clock
+ 298 1.5816 324 0.1862 vmlinux vmlinux finish_task_switch
+ 232 1.2313 231 0.1327 vmlinux vmlinux rcu_note_context_switch
+ 214 1.1358 265 0.1523 vmlinux vmlinux sub_preempt_count
+ 190 1.0084 196 0.1126 vmlinux vmlinux thumbee_notifier
--
misc: make possible to use the range field of hrtimer into the clockevent driver
https://blueprints.launchpad.net/linaro-power-kernel/+spec/hrtimer-range-and-clockevent