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powerpc: Add VDSO version of getcpu

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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>
This commit is contained in:
Anton Blanchard
2012-07-04 20:37:11 +00:00
committed by Benjamin Herrenschmidt
parent e6a74c6ea3
commit 18ad51dd34
13 changed files with 140 additions and 4 deletions
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1
arch/powerpc/include/asm/kvm_book3s_asm.h
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@@ -74,6 +74,7 @@ struct kvmppc_host_state {
ulong vmhandler;
ulong scratch0;
ulong scratch1;
ulong sprg3;
u8 in_guest;
u8 restore_hid5;
u8 napping;