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authorAnton Blanchard <anton@samba.org>2012-07-04 20:37:11 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2012-07-11 14:18:40 +1000
commit18ad51dd342a7eb09dbcd059d0b451b616d4dafc (patch)
tree94809605669eb3b5e4e049501958a2fa93ae2de7 /arch/powerpc/include/asm/reg.h
parente6a74c6ea331b79c86e1898c504790b3dadc591d (diff)
downloadlinaro-lsk-18ad51dd342a7eb09dbcd059d0b451b616d4dafc.tar.gz
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.h5
1 files changed, 3 insertions, 2 deletions
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index f0cb7f461b9..2baeb7c8764 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