Messages in this thread | | | Date | Sat, 14 Jun 2008 17:59:51 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/2] workqueues: implement flush_work() |
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On 06/14, Jarek Poplawski wrote: > > On Fri, Jun 13, 2008 at 06:28:01PM +0400, Oleg Nesterov wrote: > > (on top of [PATCH] workqueues: insert_work: use "list_head *" instead of "int tail" > > http://marc.info/?l=linux-kernel&m=121328944230175) > > > > Most of users of flush_workqueue() can be changed to use cancel_work_sync(), > > but sometimes we really need to wait for the completion and cancelling is not > > an option. schedule_on_each_cpu() is good example. > > > > Add the new helper, flush_work(work), which waits for the completion of the > > specific work_struct. > > This all looks right and better than current flush_, but... the main > problem is that probably in 90% cases cancel_ + self-running a work > function (if cancelled) should be both more efficient and safer wrt > locking (what you convince me to, BTW).
Yes, in most cases cancel_ is enough. And it is safer, note the limitations of flush_work(). Basically, flush_work(work) should be used when this work_struct can be queued only once.
> Another question is if schedule_on_each_cpu() is really such a good > example here: it seems these "xxx && yyy" examples could be faster, > but I've lost track of this earlier thread.
schedule_on_each_cpu() can't use cancel_ + ->func(), the code should be executed on the remote CPU.
And note that flush_work() doesn't iterate over all CPUs, this is the reason why it is limited, but this also means it is faster than flush_work_sync() == flush_work() + wait_on_work().
> BTW, flush_work() probably needs a lockdep annotation similar to > flush_workqueue().
Yes I know... but I'd prefer to send another patch, I'm a bit paranoid when it comes to copy-and-pasting the code.
> Otherwise this all looks OK to me.
Thanks for review!
Oleg.
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