[Resending because I forgot to CC lkml last time. Please send your replies to this thread instead of the previous (non-public) one. Sorry for the trouble!]
Hi, This patchset removes CPU hotplug's dependence on stop_machine() from the CPU offline path and provides an alternative (set of APIs) to preempt_disable() to prevent CPUs from going offline, which can be invoked from atomic context. This is an RFC patchset with only a few call-sites of preempt_disable() converted to the new APIs for now, and the main goal is to get feedback on the design of the new atomic APIs and see if it serves as a viable replacement for stop_machine()-free CPU hotplug. Overview of the patches: ----------------------- Patch 1 introduces the new APIs that can be used from atomic context, to prevent CPUs from going offline. This set of APIs is for "light" atomic hotplug readers (the term "light" is explained in the changelog/comments). Patch 2 introduces the new APIs for "full" atomic hotplug readers. Patch 3 is a cleanup; it converts preprocessor macros to static inline functions. Patches 4 to 9 convert various call-sites to use the new APIs. (Patches 4 to 8 deal with "light" readers, patch 9 deals with a "full" reader. Together, they demonstrate how to use these APIs effectively). Patch 10 is the one which actually removes stop_machine() from the CPU offline path. Changes in v2: ------------- * Completely redesigned the synchronization scheme to avoid using any extra cpumasks. * Provided APIs for 2 types of atomic hotplug readers: "light" (for light-weight) and "full". We wish to have more "light" readers than the "full" ones, to avoid indirectly inducing the "stop_machine effect" without even actually using stop_machine(). And the patches show that it _is_ generally true: 5 patches deal with "light" readers, whereas only 1 patch deals with a "full" reader. Also, the "light" readers happen to be in very hot paths. So it makes a lot of sense to have such a distinction and a corresponding light-weight API. v1: https://lkml.org/lkml/2012/12/4/88 Comments and suggestions welcome! -- Paul E. McKenney (1): cpu: No more __stop_machine() in _cpu_down() Srivatsa S. Bhat (9): CPU hotplug: Provide APIs for "light" atomic readers to prevent CPU offline CPU hotplug: Provide APIs for "full" atomic readers to prevent CPU offline CPU hotplug: Convert preprocessor macros to static inline functions smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly smp, cpu hotplug: Fix on_each_cpu_*() to prevent CPU offline properly sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() kick_process(), cpu-hotplug: Prevent offlining of target CPU properly yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly kvm, vmx: Add full atomic synchronization with CPU Hotplug arch/x86/kvm/vmx.c | 8 ++- include/linux/cpu.h | 12 ++++- kernel/cpu.c | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++- kernel/sched/core.c | 22 +++++++- kernel/smp.c | 64 +++++++++++++++--------- 5 files changed, 210 insertions(+), 32 deletions(-) Thanks, Srivatsa S. Bhat IBM Linux Technology Center -- 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/
