On Wed 01-07-15 23:06:24, Tejun Heo wrote: > Hello, Jan. > > On Wed, Jul 01, 2015 at 06:04:37PM +0200, Jan Kara wrote: > > I'd find it better to extend completions to allow doing what you need. It > > isn't that special. It seems it would be enough to implement > > > > void wait_for_completions(struct completion *x, int n); > > > > where @n is the number of completions to wait for. And the implementation > > can stay as is, only in do_wait_for_common() we change checks for x->done == > > 0 to "x->done < n". That's about it... > > I don't know. While I agree that it'd be nice to have a generic event > count & trigger mechanism in the kernel, I don't think extending > completion is a good idea - the count then works both ways as the > event counter && listener counter and effectively becomes a semaphore > which usually doesn't end well. There are very few cases where we > want the counter works both ways and I personally think we'd be far > better served if those rare cases implement something custom rather > than generic mechanism becoming cryptic trying to cover everything. Let me phrase my objection this differently: Instead of implementing custom synchronization mechanism, you could as well do: int count_submitted; /* Number of submitted works we want to wait for */ struct completion done; ... submit works with 'done' as completion. ... while (count_submitted--) wait_for_completion(&done); And we could also easily optimize that loop and put it in kernel/sched/completion.c. The less synchronization mechanisms we have the better I'd think... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
