diff options
| author | Anton Blanchard <anton@samba.org> | 2012-07-04 20:37:11 +0000 |
|---|---|---|
| committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2012-07-11 14:18:40 +1000 |
| commit | 18ad51dd342a7eb09dbcd059d0b451b616d4dafc (patch) | |
| tree | 94809605669eb3b5e4e049501958a2fa93ae2de7 /arch/powerpc/include/asm/reg.h | |
| parent | e6a74c6ea331b79c86e1898c504790b3dadc591d (diff) | |
powerpc: Add VDSO version of getcpu
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>
Diffstat (limited to 'arch/powerpc/include/asm/reg.h')
| -rw-r--r-- | arch/powerpc/include/asm/reg.h | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h index f0cb7f461b9d..2baeb7c8764f 100644 --- a/arch/powerpc/include/asm/reg.h +++ b/arch/powerpc/include/asm/reg.h @@ -491,6 +491,7 @@ #define SPRN_SPRG1 0x111 /* Special Purpose Register General 1 */ #define SPRN_SPRG2 0x112 /* Special Purpose Register General 2 */ #define SPRN_SPRG3 0x113 /* Special Purpose Register General 3 */ +#define SPRN_USPRG3 0x103 /* SPRG3 userspace read */ #define SPRN_SPRG4 0x114 /* Special Purpose Register General 4 */ #define SPRN_SPRG5 0x115 /* Special Purpose Register General 5 */ #define SPRN_SPRG6 0x116 /* Special Purpose Register General 6 */ @@ -753,14 +754,14 @@ * 64-bit server: * - SPRG0 unused (reserved for HV on Power4) * - SPRG2 scratch for exception vectors - * - SPRG3 unused (user visible) + * - SPRG3 CPU and NUMA node for VDSO getcpu (user visible) * - HSPRG0 stores PACA in HV mode * - HSPRG1 scratch for "HV" exceptions * * 64-bit embedded * - SPRG0 generic exception scratch * - SPRG2 TLB exception stack - * - SPRG3 unused (user visible) + * - SPRG3 CPU and NUMA node for VDSO getcpu (user visible) * - SPRG4 unused (user visible) * - SPRG6 TLB miss scratch (user visible, sorry !) * - SPRG7 critical exception scratch |