On Fri, 4 May 2007 00:42:26 +0400 Oleg Nesterov <[EMAIL PROTECTED]> wrote:
> Thanks to Jarek Poplawski for the ideas and for spotting the bug in the > initial draft patch. > > cancel_rearming_delayed_work() currently has many limitations, because it > requires that dwork always re-arms itself via queue_delayed_work(). So it > hangs forever if dwork doesn't do this, or cancel_rearming_delayed_work/ > cancel_delayed_work was already called. It uses flush_workqueue() in a loop, > so it can't be used if workqueue was freezed, and it is potentially live- > lockable on busy system if delay is small. > > With this patch cancel_rearming_delayed_work() doesn't make any assumptions > about dwork, it can re-arm itself via queue_delayed_work(), or queue_work(), > or do nothing. > > As a "side effect", cancel_work_sync() was changed to handle re-arming works > as well. > > Disadvantages: > > - this patch adds wmb() to insert_work(). > > - slowdowns the fast path (when del_timer() succeeds on entry) of > cancel_rearming_delayed_work(), because wait_on_work() is called > unconditionally. In that case, compared to the old version, we are > doing "unneeded" lock/unlock for each online CPU. > > On the other hand, this means we don't need to use cancel_work_sync() > after cancel_rearming_delayed_work(). > > - complicates the code (.text grows by 130 bytes). > hm, this is getting complex. > + while (!try_to_grab_pending(work)) > + ; The patch adds a couple of spinloops. Normally we put a cpu_relax() into such loops. It can make a very large difference under some circumstances. > + while (!del_timer(&dwork->timer) && > + !try_to_grab_pending(&dwork->work)) > + ; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
