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author | Davidlohr Bueso <dave@stgolabs.net> | 2020-04-23 22:48:37 -0700 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-05-13 12:14:56 -0400 |
commit | da4ad88cab5867ee240dfd0585e9d115a8cc47db (patch) | |
tree | b145ec0dedb065d2633ba62466cc5c7232a894af /arch/powerpc/kvm/powerpc.c | |
parent | 191a43be61d6791fd4a9098a35c1a09e73f55228 (diff) | |
download | linux-da4ad88cab5867ee240dfd0585e9d115a8cc47db.tar.gz |
kvm: Replace vcpu->swait with rcuwait
The use of any sort of waitqueue (simple or regular) for
wait/waking vcpus has always been an overkill and semantically
wrong. Because this is per-vcpu (which is blocked) there is
only ever a single waiting vcpu, thus no need for any sort of
queue.
As such, make use of the rcuwait primitive, with the following
considerations:
- rcuwait already provides the proper barriers that serialize
concurrent waiter and waker.
- Task wakeup is done in rcu read critical region, with a
stable task pointer.
- Because there is no concurrency among waiters, we need
not worry about rcuwait_wait_event() calls corrupting
the wait->task. As a consequence, this saves the locking
done in swait when modifying the queue. This also applies
to per-vcore wait for powerpc kvm-hv.
The x86 tscdeadline_latency test mentioned in 8577370fb0cb
("KVM: Use simple waitqueue for vcpu->wq") shows that, on avg,
latency is reduced by around 15-20% with this change.
Cc: Paul Mackerras <paulus@ozlabs.org>
Cc: kvmarm@lists.cs.columbia.edu
Cc: linux-mips@vger.kernel.org
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Message-Id: <20200424054837.5138-6-dave@stgolabs.net>
[Avoid extra logic changes. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/powerpc/kvm/powerpc.c')
-rw-r--r-- | arch/powerpc/kvm/powerpc.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index 052614e9d468..27ccff612903 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -752,7 +752,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) if (err) goto out_vcpu_uninit; - vcpu->arch.wqp = &vcpu->wq; + vcpu->arch.waitp = &vcpu->wait; kvmppc_create_vcpu_debugfs(vcpu, vcpu->vcpu_id); return 0; |