Mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/ https://git.shady.money/linux/atom?h=v3.8 2012-07-11T04:18:40Z 2012-07-11T04:18:40Z Anton Blanchard anton@samba.org 2012-07-04T20:37:11Z urn:sha1:18ad51dd342a7eb09dbcd059d0b451b616d4dafc We have a request for a fast method of getting CPU and NUMA node IDs from userspace. This patch implements a getcpu VDSO function, similar to x86. Ben suggested we use SPRG3 which is userspace readable. SPRG3 can be modified by a KVM guest, so we save the SPRG3 value in the paca and restore it when transitioning from the guest to the host. I have a glibc patch that implements sched_getcpu on top of this. Testing on a POWER7: baseline: 538 cycles vdso: 30 cycles Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>