On 12/11/2012 07:37 PM, Tejun Heo wrote: > 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. >
That's a fair point. Hmmm... Regards, Srivatsa S. Bhat -- 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/
