Andrew Morton wrote: > Did we mean to go off-list? Oops, no, pressed the wrong button.
>> Andrew Morton wrote: >>> So I'd have thought that in general an application should be querying its >>> present affinity mask - something like sched_getaffinity()? That fixes the >>> CPU hotplug issues too, of course. >> Does it really? >> >> My recollection is that the affinity masks of running processes is not >> updated on hotplugging. Is this addressed? > > ah, yes, you're correct. > > Inside a cpuset: > > sched_setaffinity() is constrained to those CPUs which are in the > cpuset. > > If a cpu if on/offlined we update each cpuset's cpu mask appropriately > but we do not update all the tasks presently running in the cpuset. > > Outside a cpuset: > > sched_setaffinity() is constrained to all possible cpus > > We don't update each task's cpus_allowed when a CPU is removed. > > > I think we trivially _could_ update each tasks's cpus_allowed mask when a > CPU is removed, actually. I think it has to be done. But that's not so trivial. What happens if all the CPUs a process was supposed to be runnable on vanish. Shouldn't, if no affinity mask is defined, new processors be added? I agree that if the process has a defined affinity mask no new processors should be added _automatically_. >> If yes, sched_getaffinity is a solution until the NUMA topology >> framework can provide something better. Even without a popcnt >> instruction in the CPU (64-bit albeit) it's twice as fast as the the >> stat() method proposed. > > I'm surprised - I'd have expected sched_getaffinity() to be vastly quicker > that doing fileystem operations. You mean because it's only a factor of two? Well, it's not once you count the whole overhead. -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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