Currently, workqueue destroys all workers for offline CPUs unless there are lingering work items. On some platforms, CPU hotplugs are used as part of runtime powersaving and thus can be very frequent. The overhead of destroying and re-creating workers on each cycle can be noticeable.
In addition, being different from the usual mode of opration, kill-all-idle involves separate driving logic, which currently is implemented across trustee_thread() and CPU hotplug notifier. This is rather complex and ugly. This patchset updates workqueue CPU hotplug path such that a disassociated global_cwq (the per-cpu worker pool) is run as if it's running as an unbound one (WQ_UNBOUND) - executing work items ASAP without concurrency management while following the usual worker management based on idle timer. While this makes rebinding somewhat more complicated, as it has to be able to rebind idle workers too, it allows overall hotplug path to be much simpler. A disassociating global_cwq simply becomes an unbound one at the end of CPU_DOWN_PREPARE and makes use of the same logic already existing for WQ_UNBOUND. While re-associating, it switches back to a bound one. Except during the transitions themselves, the usual worker management is always in effect making trustee unnecessary. 0001-workqueue-perform-cpu-down-operations-from-low-prior.patch 0002-workqueue-drop-CPU_DYING-notifier-operation.patch 0003-workqueue-ROGUE-workers-are-UNBOUND-workers.patch 0004-workqueue-use-mutex-for-global_cwq-manager-exclusion.patch 0005-workqueue-drop-bind-from-create_worker.patch 0006-workqueue-reimplement-CPU-online-rebinding-to-handle.patch 0007-workqueue-don-t-butcher-idle-workers-on-an-offline-C.patch 0008-workqueue-remove-CPU-offline-trustee.patch 0009-workqueue-simplify-CPU-hotplug-code.patch 0001 is fix for an unlikely race condition. 0002-0005 prepare for CPU hotplug reimplementation. 0006 reimplements re-binding such that it can handle idle workers too. 0007 drops killing idle workers of offline CPUs. 0008 replaces trustee with the usual management logic. 0009 refactors hotplug path a bit to clean it up. This patchset is on top of "workqueue: reimplement high priority using a separate worker pool" patchset[1] and available on the following git branch. git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git review-wq-hotplug include/linux/cpu.h | 5 kernel/workqueue.c | 738 ++++++++++++++++++++-------------------------------- 2 files changed, 296 insertions(+), 447 deletions(-) Thanks. -- tejun [1] http://lwn.net/Articles/506029/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
