Alan Cox wrote: >> Are work threads per workqueue? Combined with per-cpu binding, >> dynamic thread pool per workqueue can get quite messy. All three >> factors end up getting multiplied - ie. #cpus * pool_size which can be >> enlarged by the same work hopping around * #workqueues. > > Stop a moment. Exactly how many work queue users need per cpu binding > wizardry ? It's not about needing per-cpu binding but if works can be executed on the same cpu they were issued, it's almost always beneficial. The only reason why we have single threaded workqueue now is to limit the number of threads. >> Another problem is that if we apply this to the existing default >> workqueue which is used by many different supposed-to-be-short works >> in essentially batch mode, we might end up enlarging cache footprint >> by scheduling unnecessarily many threads, which, in tight situations, >> might show up as small but noticeable performance regression. > > Only if you make the default assumed max wait time for the work too low - > its a tunable behaviour in fact. If the default workqueue is made to manage concurrency well, most works should be able to just use it, so the queue will contain both long running ones and short running ones which can disturb the current batch like processing of the default workqueue which is assumed to have only short ones. If we maintain separate workqueues for different purposes, a tuning knob could be enough. If we try to manage the whole thing in uniform manner, a good tune might not exist. I'm not sure either way yet. One of the reasons the current situation is messy is because there are too many segregations among different thread pools (different workqueues, async thread pool, other private kthreads). It would be great if a single work API is exported and concurrency is managed automatically so that no one else has to worry about concurrency but achieving that requires much more intelligence on the workqueue implementation as the basic concurrency policies which used to be imposed by those segregations need to be handled automatically. Maybe it's better trade-off to leave those segregations as-are and just add another workqueue type with dynamic thread pool. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html