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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 /virt/kvm/kvm_main.c | |
parent | 191a43be61d6791fd4a9098a35c1a09e73f55228 (diff) | |
download | linux-stable-da4ad88cab5867ee240dfd0585e9d115a8cc47db.tar.gz linux-stable-da4ad88cab5867ee240dfd0585e9d115a8cc47db.tar.bz2 linux-stable-da4ad88cab5867ee240dfd0585e9d115a8cc47db.zip |
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 'virt/kvm/kvm_main.c')
-rw-r--r-- | virt/kvm/kvm_main.c | 19 |
1 files changed, 9 insertions, 10 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7525f3838160..e12317f32c5e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -349,7 +349,7 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id) vcpu->kvm = kvm; vcpu->vcpu_id = id; vcpu->pid = NULL; - init_swait_queue_head(&vcpu->wq); + rcuwait_init(&vcpu->wait); kvm_async_pf_vcpu_init(vcpu); vcpu->pre_pcpu = -1; @@ -2678,7 +2678,6 @@ out: void kvm_vcpu_block(struct kvm_vcpu *vcpu) { ktime_t start, cur; - DECLARE_SWAITQUEUE(wait); bool waited = false; u64 block_ns; @@ -2704,8 +2703,9 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) } while (single_task_running() && ktime_before(cur, stop)); } + prepare_to_rcuwait(&vcpu->wait); for (;;) { - prepare_to_swait_exclusive(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); + set_current_state(TASK_INTERRUPTIBLE); if (kvm_vcpu_check_block(vcpu) < 0) break; @@ -2713,8 +2713,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) waited = true; schedule(); } - - finish_swait(&vcpu->wq, &wait); + finish_rcuwait(&vcpu->wait); cur = ktime_get(); out: kvm_arch_vcpu_unblocking(vcpu); @@ -2746,11 +2745,10 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_block); bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu) { - struct swait_queue_head *wqp; + struct rcuwait *waitp; - wqp = kvm_arch_vcpu_wq(vcpu); - if (swq_has_sleeper(wqp)) { - swake_up_one(wqp); + waitp = kvm_arch_vcpu_get_wait(vcpu); + if (rcuwait_wake_up(waitp)) { WRITE_ONCE(vcpu->ready, true); ++vcpu->stat.halt_wakeup; return true; @@ -2892,7 +2890,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) continue; if (vcpu == me) continue; - if (swait_active(&vcpu->wq) && !vcpu_dy_runnable(vcpu)) + if (rcuwait_active(&vcpu->wait) && + !vcpu_dy_runnable(vcpu)) continue; if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu)) |