[PATCHSET sched/core] cpuhog: implement and use cpuhog, take#2
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From: Tejun Heo on 17 Mar 2010 04:50 Hello, This is the second take of cpuhog patchset which implements a simplistic cpu monopolization mechanism and reimplements stop_machine() and replaces migration_thread with it. This allows stop_machine() to be simpler and much more efficient on very large machines without using more resources while also making the rather messy overloaded migration_thread usages cleaner. This should solve the slow boot problem[1] caused by repeated stop_machine workqueue creation/destruction reported by Dimitri Sivanich. Changes from the last take[L] are * cpuhog callbacks are no longer allowed to sleep. preemption is disabled around them. * Patches are rebased on top of sched/core. This patchset contains the following four patches. 0001-cpuhog-implement-cpuhog.patch 0002-stop_machine-reimplement-using-cpuhog.patch 0003-scheduler-replace-migration_thread-with-cpuhog.patch 0004-scheduler-kill-paranoia-check-in-synchronize_sched_e.patch Tested cpu on/offlining, shutdown, all migration usage paths including RCU torture test at 0003 and 004 and everything seems to work fine here. Peter suggested reusing stop_cpu/machine() names instead of introducing new hog_* names. While renaming definitely is an option, I think it's better to keep the distinction between stop_{cpu|machine}() and this maximum priority scheduler based monopolization mechanism. hog_[one_]cpu[s]() schedule highest priority task to monopolize the upper half of cpu[s] but doesn't affect contextless part of the cpu (hard/soft irq, bh, tasklet...) nor does it coordinate with each other to make sure all the cpus are synchronized while executing the callbacks. In that sense, it is the lowest bottom of upper half but not quite stopping the cpu or the machine and I think the distinction is meaningful to make. Now that the callbacks are not allowed to sleep, they really 'hog' the target cpus too. I wanted to avoid verbs associated with the traditional workqueue - schedule and queue, while emphasizing that this is something that you don't want to abuse - so the verb hog. monopolize_cpu() was the second choice but hog is shorter and can be used as a noun as-is, so I chose hog. If you like/dislike the name, please let me know. If Rusty and RCU people agree (where are you? :-), I think it would be the easiest to route the whole thing through sched tree so I rebased it on top of sched/core. Again, if you disagree, please let me know. The tree is available in the following git tree. git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git cpuhog diffstat follows. Documentation/RCU/torture.txt | 10 - arch/s390/kernel/time.c | 1 drivers/xen/manage.c | 14 - include/linux/cpuhog.h | 24 ++ include/linux/rcutiny.h | 2 include/linux/rcutree.h | 1 include/linux/stop_machine.h | 20 -- kernel/Makefile | 2 kernel/cpu.c | 8 kernel/cpuhog.c | 368 ++++++++++++++++++++++++++++++++++++++++++ kernel/module.c | 14 - kernel/rcutorture.c | 2 kernel/sched.c | 282 +++++--------------------------- kernel/sched_fair.c | 39 ++-- kernel/stop_machine.c | 162 ++++-------------- 15 files changed, 511 insertions(+), 438 deletions(-) Thanks. -- tejun [1] http://thread.gmane.org/gmane.linux.kernel/957726 [L] http://thread.gmane.org/gmane.linux.kernel/958743 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |