On 10/10, Andrew Morton wrote: > > On Thu, 10 Oct 2013 17:26:12 +0200 Oleg Nesterov <o...@redhat.com> wrote: > > > On 10/10, Ingo Molnar wrote: > > > > > > So ... why not make it _really_ cheap, i.e. the read lock costing nothing, > > > and tie CPU hotplug to freezing all tasks in the system? > > > > > > Actual CPU hot unplugging and repluggin is _ridiculously_ rare in a > > > system, I don't understand how we tolerate _any_ overhead from this utter > > > slowpath. > > > > Well, iirc Srivatsa (cc'ed) pointed out that some systems do cpu_down/up > > quite often to save the power. > > cpu hotremove already uses stop_machine,
And Srivatsa wants to remove it from cpu_down(). > so such an approach shouldn't > actually worsen things (a lot) for them? this depends on what this "freezing all tasks" actually means. I understood it as try_to_freeze_tasks/etc, looks too heavy... But my only point was, I am not sure we can assume that cpu_down/up is extremly rare and its cost does not matter. > use stop_machine() on the add/remove > (ie, "writer") side and nothing at all on the "reader" side. Is there > anything which fundamentally prevents cpu hotplug from doing the same? Well, then we actually need to park all tasks in system, I guess. IOW, freezer. Oleg. -- 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/
