On Fri, Jul 10, 2015 at 03:05:02PM -0400, Chris Metcalf wrote: > On 07/10/2015 02:24 PM, Frederic Weisbecker wrote: > >Indeed we are doing more and more references on housekeeping_mask, so > >we should probably think about an off-case. > > > >Now the nohz-full off-case should rather be cpu_possible_mask than > >cpu_online_mask. housekeeping_mask doesn't take into account onlining > >at all. > > That suggests that in this case, we might want to default to > something like "housekeeping_mask & cpu_online_mask", > since you really don't want to send irqs to offline cores to > process your packets :-)
In any case it must be up to the drivers to do that. Define housekeeping_mask as a subset of the online mask complicates a lot of things. It pushes hotplug complexity to the nohz code for no reasons. It's up to the drivers and subsystems to handle that really. > > The tilegx chips typically don't do cpu offlining anyway, since > we've never really found a usecase, so whatever you boot with > you always have available. We do have support for a bare-metal > mode which you can run on some of the cores, so you may start > with fewer than cpu_possible actually running, but it will always > be that same set of cores. And that bare metal mode runs out of Linux? Note that in nohz_full, The boot CPU can't be offline anyway. > > So this does suggest that my original patch is wrong for that > same reason. > > >>2. Provide an accessor that returns the cpumask to use for housekeeping > >> chores and implement it in the obvious ways for both nohz_full > >> and non-nohz_full. > >> > >>The latter seems like arguably the most satisfying approach, but > >>the patch below is, if nothing else, suitable to push for 4.3 > >>without any further API development work. > >I don't know. 1) looks easier. > > On reflection, the problem with (1) is that if you are in NO_HZ_FULL > mode but !tick_nohz_full_enabled(), you want to fall back to just > using cpu_possible_mask anyway. So I think a simple accessor that > returns an appropriate cpumask pointer is probably the best bet > (along the lines of the existing is_housekeeping_cpu() accessor). Ok! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
