On Wed, 2009-03-18 at 18:17 -0700, David Miller wrote: > From: Sven-Thorsten Dietrich <sven@xxxxxxxxxxxxxxxxxxxxx> > Date: Wed, 18 Mar 2009 18:13:11 -0700 > > > On Wed, 2009-03-18 at 18:03 -0700, David Miller wrote: > > > From: Gregory Haskins <ghaskins@xxxxxxxxxx> > > > Date: Wed, 18 Mar 2009 17:54:04 -0400 > > > > > > > Note that -rt doesnt typically context-switch under contention anymore > > > > since we introduced adaptive-locks. Also note that the contention > > > > against the lock is still contention, regardless of whether you have -rt > > > > or not. Its just that the slow-path to handle the contended case for > > > > -rt is more expensive than mainline. However, once you have the > > > > contention as stated, you have already lost. > > > > > > First, contention is not implicitly a bad thing. > > > > Its a bad thing when it does not scale. > > You have only one pipe to shove packets into in this case, and for > your workload multiple cpus are going to be trying to stuff a single > packet at a time from a single UDP send request. > > There is no added parallelism you can create for that kind of workload > on that kind of hardware. > Do we have to rule-out per-CPU queues, that aggregate into a master queue in a batch-wise manner? I speculate that might reduce the lock contention by a factor of NCPUs. I cannot say this would be enough to mitigate the consequent overhead penalty. > It is one of the issues addressed by multiqueue. Properly tuned adaptive locks, would theoretically perform near-optimally compared to the mainline case, and would provide better CPU utilization on very large parallel architectures. Sven -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
