The information in /sys/devices/system/cpu/cpuX/topology directory is useful for userspace monitoring applications and in-tree utilities like cpupower & turbostat.
When down'ing a CPU the /sys/devices/system/cpu/cpuX/topology directory is removed during the CPU_DEAD hotplug callback in the kernel. The problem with this model is that the CPU has not been physically removed and the data in the topology directory is still valid. IOW, the cpu is still present but the kernel has removed the topology directory making it very difficult to determine exactly where the cpu is located. This patchset adds CONFIG_PERMANENT_CPU_TOPOLOGY, and is Y by default for x86, an N for all other arches. When enabled the kernel is modified so that the topology directory is added to the core cpu sysfs files so that the topology directory exists for the lifetime of the CPU. When disabled, the behavior of the current kernel is maintained (that is, the topology directory is removed on a down and added on an up). Adding CONFIG_PERMANENT_CPU_TOPOLOGY may require additional architecture so that the cpumask data the CPU's topology is not cleared during a CPU down. This patchset combines drivers/base/topology.c and drivers/base/cpu.c to implement CONFIG_PERMANENT_CPU_TOPOLOGY and leaves all arches except x86 with the current behavior. peterz asked when the topology directory is destroyed when CONFIG_PERMANENT_CPU_TOPOLOGY=y. The topology directory's lifetime will change when CONFIG_PERMANENT_CPU_TOPOLOGY=y from existing when the thread is online, to being created when the struct device associated with the thread is created, and similarly being destroyed when the struct device is destroyed. [v2 & v3]: Fix ktest build robot build failures Signed-off-by: Prarit Bhargava <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: [email protected] Cc: Greg Kroah-Hartman <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Len Brown <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Jiri Olsa <[email protected]> Cc: Juergen Gross <[email protected]> Prarit Bhargava (2): drivers/base: Combine topology.c and cpu.c cpu hotplug: add CONFIG_PERMANENT_CPU_TOPOLOGY arch/x86/kernel/smpboot.c | 3 - drivers/base/Kconfig | 12 ++++ drivers/base/Makefile | 2 +- drivers/base/cpu.c | 148 +++++++++++++++++++++++++++++++++++++++ drivers/base/topology.c | 168 --------------------------------------------- 5 files changed, 161 insertions(+), 172 deletions(-) delete mode 100644 drivers/base/topology.c -- 1.7.9.3
