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powerpc/64s/idle: avoid sync for KVM state when waking from idle

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When waking from a CPU idle instruction (e.g., nap or stop), the sync
for ordering the KVM secondary thread state can be avoided if there
wakeup is coming from a kernel context rather than KVM context.

This improves performance for ping-pong benchmark with the stop0 idle
state by 0.46% for 2 threads in the same core, and 1.02% for different
cores.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2017-11-18 00:08:06 +10:00 committed by Michael Ellerman
parent 3d4fbffdd7
commit 8c1c7fb0b5
1 changed files with 3 additions and 0 deletions
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3
arch/powerpc/kernel/idle_book3s.S
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@ -551,6 +551,9 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
mr r3,r12
#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
lbz r0,HSTATE_HWTHREAD_STATE(r13)
cmpwi r0,KVM_HWTHREAD_IN_KERNEL
beq 1f
li r0,KVM_HWTHREAD_IN_KERNEL
stb r0,HSTATE_HWTHREAD_STATE(r13)
/* Order setting hwthread_state vs. testing hwthread_req */