Hi All,
This is V2 of my sched_select_cpu() work.
In order to save power, it would be useful to schedule work onto non-IDLE cpus instead of waking up an IDLE one.
To achieve this, we need scheduler to guide kernel frameworks (like: timers & workqueues) on which is the most preferred CPU that must be used for these tasks.
This patchset is about implementing this concept.
- The first patch adds sched_select_cpu() routine which returns the preferred cpu which is non-idle. - Second patch removes idle_cpu() calls from timer & hrtimer. - Third patch is about adapting this change in workqueue framework.
Earlier discussions over v1 can be found here: http://www.mail-archive.com/linaro-dev@lists.linaro.org/msg13342.html
Earlier discussions over this concept were done at last LPC: http://summit.linuxplumbersconf.org/lpc-2012/meeting/90/lpc2012-sched-timer-...
Module created for testing this behavior is present here: http://git.linaro.org/gitweb?p=people/vireshk/module.git%3Ba=summary
Following are the steps followed in test module: 1. Run single work on each cpu 2. This work will start a timer after x (tested with 10) jiffies of delay 3. Timer routine queues a work... (This may be called from idle or non-idle cpu) and starts the same timer again STEP 3 is done for n number of times (i.e. queuing n works, one after other) 4. All works will call a single routine, which will count following per cpu: - Total works processed by a CPU - Total works processed by a CPU, which are queued from it - Total works processed by a CPU, which aren't queued from it
Setup: ----- - ARM Vexpress TC2 - big.LITTLE CPU - Core 0-1: A15, 2-4: A7 - rootfs: linaro-ubuntu-nano
Results: ------- Without Workqueue Modification, i.e. PATCH 3/3: [ 2493.022335] Workqueue Analyser: works processsed by CPU0, Total: 1000, Own: 0, migrated: 0 [ 2493.047789] Workqueue Analyser: works processsed by CPU1, Total: 1000, Own: 0, migrated: 0 [ 2493.072918] Workqueue Analyser: works processsed by CPU2, Total: 1000, Own: 0, migrated: 0 [ 2493.098576] Workqueue Analyser: works processsed by CPU3, Total: 1000, Own: 0, migrated: 0 [ 2493.123702] Workqueue Analyser: works processsed by CPU4, Total: 1000, Own: 0, migrated: 0
With Workqueue Modification, i.e. PATCH 3/3: [ 2493.022335] Workqueue Analyser: works processsed by CPU0, Total: 1002, Own: 999, migrated: 3 [ 2493.047789] Workqueue Analyser: works processsed by CPU1, Total: 998, Own: 997, migrated: 1 [ 2493.072918] Workqueue Analyser: works processsed by CPU2, Total: 1013, Own: 996, migrated: 17 [ 2493.098576] Workqueue Analyser: works processsed by CPU3, Total: 998, Own: 993, migrated: 5 [ 2493.123702] Workqueue Analyser: works processsed by CPU4, Total: 989, Own: 987, migrated: 2
V1->V2 ----- - New SD_* macros removed now and earlier ones used - sched_select_cpu() rewritten and it includes the check on current cpu's idleness. - cpu_idle() calls from timer and hrtimer removed now. - Patch 2/3 from V1, removed as it doesn't apply to latest workqueue branch from tejun. - CONFIG_MIGRATE_WQ removed and so is wq_select_cpu() - sched_select_cpu() called only from __queue_work() - got tejun/for-3.7 branch in my tree, before making workqueue changes.
Viresh Kumar (3): sched: Create sched_select_cpu() to give preferred CPU for power saving timer: hrtimer: Don't check idle_cpu() before calling get_nohz_timer_target() workqueue: Schedule work on non-idle cpu instead of current one
include/linux/sched.h | 16 ++++++++++-- kernel/hrtimer.c | 2 +- kernel/sched/core.c | 69 +++++++++++++++++++++++++++++++-------------------- kernel/timer.c | 9 ++++--- kernel/workqueue.c | 2 +- 5 files changed, 63 insertions(+), 35 deletions(-)