On Mon, Jul 21, 2014 at 08:57:41AM -0700, Paul E. McKenney wrote: > On Sun, Jul 20, 2014 at 10:34:17PM +0200, Peter Zijlstra wrote: > > On Sun, Jul 20, 2014 at 04:47:59AM -0700, Paul E. McKenney wrote: > > > So we really have to have -all- the CPUs be idle to turn off the > > > timekeeper. > > > > That seems to be pretty unavoidable any which way around. > > Hmmm... The exception would be the likely common case where none of > the CPUs are flagged as nohz_full= CPUs. If we handled that case as > if CONFIG_NO_HZ_FULL=n, we would have handled almost all of > the problem.
Exactly, like you said on a further post, tick_nohz_full_enabled() is the magic you need :) > > > > This won't make the battery-powered embedded guys happy... > > > > > > Other thoughts on this? We really should not be setting > > > CONFIG_NO_HZ_FULL_SYSIDLE by default until this is solved. > > > > What are those same guys doing with nohz_full to begin with? > > If CONFIG_NO_HZ_FULL_SYSIDLE=y is the default, my main concern is for > people who didn't really want it, and who thus did not set the nohz_full= > boot parameter. Hence my suggestion above that we treat that case as > if CONFIG_NO_HZ_FULL=n (and thus also as if CONFIG_NO_HZ_FULL_SYSIDLE=n). > > There have been some people saying that they want only a subset of > their CPUs in nohz_full= state, and these guys seem to want to run a > mixed workload. For example, they have HPC (or RT) workloads on the > nohz_full= CPUs, and also want normal high-throughput processing on the > remaining CPUs. If software was trivial (and making other unlikely > assumptions about the perfection of the world and the invalidity of > Murphy's lawy), we would want the timekeeping CPU to be able to move > among the non-nohz_full= CPUs. > > However, this should be a small fraction of the users, and many of > these guys would probably be open to making a few changes. Thus, a > less-proactive approach should allow us to solve their actual problems, as > opposed to the problems that we speculate that they might encounter. ;-) Sounds pretty good way of doing things! > Thanx, Paul > -- 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/
