On Thu, 2011-08-11 at 12:54 -0700, Mike Turquette wrote: > On some platforms it is possible to have some CPUs which support CPU > hotplug and some which do not. Currently the prescence of an 'online' > sysfs entry in userspace is adequate for applications to know that a CPU > supports hotplug, but there is no convenient way to make the same > determination in the kernel. > > To better model this relationship this patch introduces a new cpumask to > track CPUs that support CPU hotplug operations. > > This new cpumask is populated at boot-time and remains static for the > life of the machine. Bits set in the mask indicate a CPU which supports > hotplug, but make no guarantees about whether that CPU is currently > online or not. Likewise a cleared bit in the mask indicates either a > CPU which cannot hotplug or a lack of a populated CPU. > > The purpose of this new cpumask is to aid kernel code which uses CPU to > take CPUs online and offline. Possible uses are as a thermal event > mitigation technique or as a power capping mechanism. Nacked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> the kernel really shouldn't be using hotplug for this (nor should userspace really). hot-unplugging random cpus wrecks things like cpusets. Furthermore hotplug does way too much work to use as a simple means to idle a cpu. Even the availability of this mask is wrong, since that implies the information is useful, which per the above it is not, the kernel shouldn't care about this full-stop. The only reason for the OS to unplug a CPU is imminent and unavoidable hardware failure. Thermal capping is not that (and yes ACPI-4.0 is a broken piece of shit). _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
