From patchwork Fri Mar 20 08:55:26 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Davidlohr Bueso X-Patchwork-Id: 11448627 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7747E1392 for ; Fri, 20 Mar 2020 08:56:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 53C9D20767 for ; Fri, 20 Mar 2020 08:56:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727052AbgCTI4r (ORCPT ); Fri, 20 Mar 2020 04:56:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:43382 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726232AbgCTI4q (ORCPT ); Fri, 20 Mar 2020 04:56:46 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 21A8FAEE2; Fri, 20 Mar 2020 08:56:44 +0000 (UTC) From: Davidlohr Bueso To: tglx@linutronix.de Cc: arnd@arndb.de, balbi@kernel.org, bhelgaas@google.com, bigeasy@linutronix.de, dave@stgolabs.net, davem@davemloft.net, gregkh@linuxfoundation.org, joel@joelfernandes.org, kurt.schwemmer@microsemi.com, kvalo@codeaurora.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-usb@vger.kernel.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, logang@deltatee.com, mingo@kernel.org, mpe@ellerman.id.au, netdev@vger.kernel.org, oleg@redhat.com, paulmck@kernel.org, peterz@infradead.org, rdunlap@infradead.org, rostedt@goodmis.org, torvalds@linux-foundation.org, will@kernel.org, Paolo Bonzini , Davidlohr Bueso Subject: [PATCH 18/15] kvm: Replace vcpu->swait with rcuwait Date: Fri, 20 Mar 2020 01:55:26 -0700 Message-Id: <20200320085527.23861-3-dave@stgolabs.net> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200320085527.23861-1-dave@stgolabs.net> References: <20200318204302.693307984@linutronix.de> <20200320085527.23861-1-dave@stgolabs.net> Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org 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 adding to the queue. 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% with this change. Cc: Paolo Bonzini Signed-off-by: Davidlohr Bueso --- Only compiled and tested on x86. arch/powerpc/include/asm/kvm_host.h | 2 +- arch/powerpc/kvm/book3s_hv.c | 10 ++++------ arch/x86/kvm/lapic.c | 2 +- include/linux/kvm_host.h | 10 +++++----- virt/kvm/arm/arch_timer.c | 2 +- virt/kvm/arm/arm.c | 9 +++++---- virt/kvm/async_pf.c | 3 +-- virt/kvm/kvm_main.c | 33 +++++++++++++-------------------- 8 files changed, 31 insertions(+), 40 deletions(-) diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index 6e8b8ffd06ad..e2b4a1e3fb7d 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -752,7 +752,7 @@ struct kvm_vcpu_arch { u8 irq_pending; /* Used by XIVE to signal pending guest irqs */ u32 last_inst; - struct swait_queue_head *wqp; + struct rcuwait *waitp; struct kvmppc_vcore *vcore; int ret; int trap; diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 2cefd071b848..c7cbc4bd06e9 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -231,13 +231,11 @@ static bool kvmppc_ipi_thread(int cpu) static void kvmppc_fast_vcpu_kick_hv(struct kvm_vcpu *vcpu) { int cpu; - struct swait_queue_head *wqp; + struct rcuwait *wait; - wqp = kvm_arch_vcpu_wq(vcpu); - if (swq_has_sleeper(wqp)) { - swake_up_one(wqp); + wait = kvm_arch_vcpu_get_wait(vcpu); + if (rcuwait_wake_up(wait)) ++vcpu->stat.halt_wakeup; - } cpu = READ_ONCE(vcpu->arch.thread_cpu); if (cpu >= 0 && kvmppc_ipi_thread(cpu)) @@ -4274,7 +4272,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) } user_vrsave = mfspr(SPRN_VRSAVE); - vcpu->arch.wqp = &vcpu->arch.vcore->wq; + vcpu->arch.waitp = &vcpu->arch.vcore->wait; vcpu->arch.pgdir = kvm->mm->pgd; vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST; diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index e3099c642fec..a4420c26dfbc 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1815,7 +1815,7 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu) /* If the preempt notifier has already run, it also called apic_timer_expired */ if (!apic->lapic_timer.hv_timer_in_use) goto out; - WARN_ON(swait_active(&vcpu->wq)); + WARN_ON(rcu_dereference(vcpu->wait.task)); cancel_hv_timer(apic); apic_timer_expired(apic); diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index bcb9b2ac0791..b5694429aede 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -23,7 +23,7 @@ #include #include #include -#include +#include #include #include #include @@ -277,7 +277,7 @@ struct kvm_vcpu { struct mutex mutex; struct kvm_run *run; - struct swait_queue_head wq; + struct rcuwait wait; struct pid __rcu *pid; int sigset_active; sigset_t sigset; @@ -952,12 +952,12 @@ static inline bool kvm_arch_has_assigned_device(struct kvm *kvm) } #endif -static inline struct swait_queue_head *kvm_arch_vcpu_wq(struct kvm_vcpu *vcpu) +static inline struct rcuwait *kvm_arch_vcpu_get_wait(struct kvm_vcpu *vcpu) { #ifdef __KVM_HAVE_ARCH_WQP - return vcpu->arch.wqp; + return vcpu->arch.wait; #else - return &vcpu->wq; + return &vcpu->wait; #endif } diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c index 0d9438e9de2a..4be71cb58691 100644 --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -593,7 +593,7 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) if (map.emul_ptimer) soft_timer_cancel(&map.emul_ptimer->hrtimer); - if (swait_active(kvm_arch_vcpu_wq(vcpu))) + if (rcu_dereference(kvm_arch_vpu_get_wait(vcpu)) != NULL) kvm_timer_blocking(vcpu); /* diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index eda7b624eab8..4a704866e9b6 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -579,16 +579,17 @@ void kvm_arm_resume_guest(struct kvm *kvm) kvm_for_each_vcpu(i, vcpu, kvm) { vcpu->arch.pause = false; - swake_up_one(kvm_arch_vcpu_wq(vcpu)); + rcuwait_wake_up(kvm_arch_vcpu_get_wait(vcpu)); } } static void vcpu_req_sleep(struct kvm_vcpu *vcpu) { - struct swait_queue_head *wq = kvm_arch_vcpu_wq(vcpu); + struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu); - swait_event_interruptible_exclusive(*wq, ((!vcpu->arch.power_off) && - (!vcpu->arch.pause))); + rcuwait_wait_event(*wait, + (!vcpu->arch.power_off) && (!vcpu->arch.pause), + TASK_INTERRUPTIBLE); if (vcpu->arch.power_off || vcpu->arch.pause) { /* Awaken to handle a signal, request we sleep again later. */ diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 15e5b037f92d..10b533f641a6 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -80,8 +80,7 @@ static void async_pf_execute(struct work_struct *work) trace_kvm_async_pf_completed(addr, cr2_or_gpa); - if (swq_has_sleeper(&vcpu->wq)) - swake_up_one(&vcpu->wq); + rcuwait_wake_up(&vcpu->wait); mmput(mm); kvm_put_kvm(vcpu->kvm); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 70f03ce0e5c1..6b49dcb321e2 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -343,7 +343,7 @@ 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; @@ -2465,9 +2465,8 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu) void kvm_vcpu_block(struct kvm_vcpu *vcpu) { ktime_t start, cur; - DECLARE_SWAITQUEUE(wait); - bool waited = false; u64 block_ns; + int block_check = -EINTR; kvm_arch_vcpu_blocking(vcpu); @@ -2487,21 +2486,14 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) ++vcpu->stat.halt_poll_invalid; goto out; } + cur = ktime_get(); } while (single_task_running() && ktime_before(cur, stop)); } - for (;;) { - prepare_to_swait_exclusive(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); - - if (kvm_vcpu_check_block(vcpu) < 0) - break; - - waited = true; - schedule(); - } - - finish_swait(&vcpu->wq, &wait); + rcuwait_wait_event(&vcpu->wait, + (block_check = kvm_vcpu_check_block(vcpu)) < 0, + TASK_INTERRUPTIBLE); cur = ktime_get(); out: kvm_arch_vcpu_unblocking(vcpu); @@ -2525,18 +2517,18 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) } } - trace_kvm_vcpu_wakeup(block_ns, waited, vcpu_valid_wakeup(vcpu)); + trace_kvm_vcpu_wakeup(block_ns, block_check < 0 ? false : true, + vcpu_valid_wakeup(vcpu)); kvm_arch_vcpu_block_finish(vcpu); } EXPORT_SYMBOL_GPL(kvm_vcpu_block); bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu) { - struct swait_queue_head *wqp; + struct rcuwait *wait; - wqp = kvm_arch_vcpu_wq(vcpu); - if (swq_has_sleeper(wqp)) { - swake_up_one(wqp); + wait = kvm_arch_vcpu_get_wait(vcpu); + if (rcuwait_wake_up(wait)) { WRITE_ONCE(vcpu->ready, true); ++vcpu->stat.halt_wakeup; return true; @@ -2678,7 +2670,8 @@ 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 (rcu_dereference(vcpu->wait.task) && + !vcpu_dy_runnable(vcpu)) continue; if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu))