Messages in this thread Patch in this message | | | Date | Tue, 18 Sep 2012 13:49:34 -0700 | From | Tejun Heo <> | Subject | [PATCH 3.6-rc6 1/2] workqueue: reimplement work_on_cpu() using system_wq |
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The existing work_on_cpu() implementation is hugely inefficient. It creates a new kthread, execute that single function and then let the kthread die on each invocation.
Now that system_wq can handle concurrent executions, there's no advantage of doing this. Reimplement work_on_cpu() using system_wq which makes it simpler and way more efficient.
stable: While this isn't a fix in itself, it's needed to fix a workqueue related bug in cpufreq/powernow-k8. AFAICS, this shouldn't break other existing users.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Len Brown <lenb@kernel.org> Cc: Rafael J. Wysocki <rjw@sisk.pl> Cc: stable@vger.kernel.org --- So, here are the two patches which can be applied to 3.6-rc6. I'll post a combined patch to the bugzilla so that Duncan can test it.
The only worrying thing is that this might affect the existing work_on_cpu() users in some crazy subtle way. I can't see how it would break anything but it's when I think like that when something bites me. That said, pci-driver is probably the most common use case and it seems to work fine here.
Thanks.
kernel/workqueue.c | 27 +++++++++------------------ 1 file changed, 9 insertions(+), 18 deletions(-)
--- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3576,18 +3576,17 @@ static int __devinit workqueue_cpu_down_ #ifdef CONFIG_SMP struct work_for_cpu { - struct completion completion; + struct work_struct work; long (*fn)(void *); void *arg; long ret; }; -static int do_work_for_cpu(void *_wfc) +static void work_for_cpu_fn(struct work_struct *work) { - struct work_for_cpu *wfc = _wfc; + struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work); + wfc->ret = wfc->fn(wfc->arg); - complete(&wfc->completion); - return 0; } /** @@ -3602,19 +3601,11 @@ static int do_work_for_cpu(void *_wfc) */ long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg) { - struct task_struct *sub_thread; - struct work_for_cpu wfc = { - .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion), - .fn = fn, - .arg = arg, - }; - - sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu"); - if (IS_ERR(sub_thread)) - return PTR_ERR(sub_thread); - kthread_bind(sub_thread, cpu); - wake_up_process(sub_thread); - wait_for_completion(&wfc.completion); + struct work_for_cpu wfc = { .fn = fn, .arg = arg }; + + INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn); + schedule_work_on(cpu, &wfc.work); + flush_work(&wfc.work); return wfc.ret; } EXPORT_SYMBOL_GPL(work_on_cpu);
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