On Mon, May 19, 2014 at 04:44:41AM +0200, Mike Galbraith wrote: > On Sun, 2014-05-18 at 08:58 -0700, Paul E. McKenney wrote: > > On Sun, May 18, 2014 at 10:36:41AM +0200, Mike Galbraith wrote: > > > On Sat, 2014-05-17 at 22:20 -0700, Paul E. McKenney wrote: > > > > > > > If you are saying that turning on nohz_full doesn't help unless you > > > > also ensure that there is only one runnable task per CPU, I completely > > > > agree. If you are saying something else, you lost me. ;-) > > > > > > Yup, that's it more or less. It's not only single task loads that could > > > benefit from better isolation, but if isolation improving measures are > > > tied to nohz_full, other sensitive loads will suffer if they try to use > > > isolation improvements. > > > > So you are arguing for a separate Kconfig variable that does the isolation? > > So that NO_HZ_FULL selects this new variable, and (for example) RCU > > uses this new variable to decide when to pin the grace-period kthreads > > onto the housekeeping CPU? > > I'm thinking more about runtime, but yes. > > The tick mode really wants to be selectable per set (in my boxen you can > switch between nohz off/idle, but not yet nohz_full, that might get real > interesting). You saw in my numbers that ticked is far better for the > threaded rt load, but what if the total load has both sensitive rt and > compute components to worry about? The rt component wants relief from > the jitter that flipping the tick inflicts, but also wants as little > disturbance as possible, so RCU offload and whatever other measures that > are or become available are perhaps interesting to it as well. The > numbers showed that here and now the two modes can work together in the > same box, I can have my rt set ticking away, and other cores doing > tickless compute, but enabling that via common config (distros don't > want to ship many kernel flavors) has a cost to rt performance. > > Ideally, bean counting would be switchable too, giving all components > the environment they like best. Sounds like a question for Frederic (now CCed). ;-) Thanx, Paul -- 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
