Hello, On Tue, Dec 11, 2012 at 07:32:13PM +0530, Srivatsa S. Bhat wrote: > On 12/11/2012 07:17 PM, Tejun Heo wrote: > > Hello, Srivatsa. > > > > On Tue, Dec 11, 2012 at 06:43:54PM +0530, Srivatsa S. Bhat wrote: > >> This approach (of using synchronize_sched()) also looks good. It is simple, > >> yet effective, but unfortunately inefficient at the writer side (because > >> he'll have to wait for a full synchronize_sched()). > > > > While synchornize_sched() is heavier on the writer side than the > > originally posted version, it doesn't stall the whole machine and > > wouldn't introduce latencies to others. Shouldn't that be enough? > > > > Short answer: Yes. But we can do better, with almost comparable code > complexity. So I'm tempted to try that out. > > Long answer: > Even in the synchronize_sched() approach, we still have to identify the > readers who need to be converted to use the new get/put_online_cpus_atomic() > APIs and convert them. Then, if we can come up with a scheme such that > the writer has to wait only for those readers to complete, then why not? > > If such a scheme ends up becoming too complicated, then I agree, we > can use synchronize_sched() itself. (That's what I meant by saying that > we'll use this as a fallback). > > But even in this scheme which uses synchronize_sched(), we are > already half-way through (we already use 2 types of sync schemes - > counters and rwlocks). Just a little more logic can get rid of the > unnecessary full-wait too.. So why not give it a shot?
It's not really about the code complexity but making the reader side as light as possible. Please keep in mind that reader side is still *way* more hotter than the writer side. Before, the writer side was heavy to the extent which causes noticeable disruptions on the whole system and I think that's what we're trying to hunt down here. If we can shave of memory barriers from reader side by using synchornized_sched() on writer side, that is the *better* result, not worse. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
