• Anton Blanchard's avatar
    powerpc: Add VDSO version of getcpu · 18ad51dd
    Anton Blanchard authored
    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: default avatarAnton Blanchard <anton@samba.org>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    18ad51dd
kvm_book3s_asm.h 3.23 KB