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([2408:822f:1aba:84a0:651:104c:ba0c:1f4a]) by smtp.googlemail.com with ESMTPSA id 98e67ed59e1d1-37a1f07bbfdsm250713a91.5.2026.06.11.18.34.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Jun 2026 18:34:41 -0700 (PDT) From: Wanpeng Li To: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Paolo Bonzini , Sean Christopherson Cc: K Prateek Nayak , Christian Borntraeger , Steven Rostedt , Vincent Guittot , Juri Lelli , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Wanpeng Li , Richie Buturla Subject: [PATCH v3 09/10] KVM: Add IPI-aware directed-yield candidate selection Date: Fri, 12 Jun 2026 09:33:54 +0800 Message-ID: <20260612013355.59231-10-kernellwp@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260612013355.59231-1-kernellwp@gmail.com> References: <20260612013355.59231-1-kernellwp@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Wanpeng Li kvm_vcpu_on_spin() selects a directed-yield target from coarse preempted and preempted-in-kernel state. It cannot distinguish a vCPU spinning on an IPI response from a vCPU spinning on a lock, and can therefore yield to an unrelated vCPU. Add kvm_vcpu_is_good_yield_candidate(), a priority-ordered filter. Prefer a confirmed recent IPI receiver of the spinning vCPU, then an arch-provided pending-interrupt hint, and finally the existing preempted heuristic with the optional in-kernel filter. Use the helper in the strict scan before falling back to the existing directed-yield eligibility checks. Signed-off-by: Wanpeng Li --- virt/kvm/kvm_main.c | 65 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 55 insertions(+), 10 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 2e11c6cfc167..84cbd7a6183f 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3963,12 +3963,51 @@ bool __weak kvm_vcpu_is_ipi_receiver(struct kvm_vcpu *sender, return false; } +/* + * Priority-based candidate filter for directed yield. + * + * 1) Confirmed IPI receiver of @me within the recency window. + * This is the highest-confidence signal that selecting @vcpu + * may help @me complete its spin-on-IPI-response. + * 2) Arch-provided fast pending-interrupt hint (APICv / AVIC / + * arch_dy_has_pending_interrupt()). Covers cases where IPI + * tracking was bypassed by hardware acceleration. + * 3) Legacy preempted fallback, with the existing optional + * in-kernel filter when @yield_to_kernel_mode is set. + * + * Returning false asks kvm_vcpu_on_spin() to skip @vcpu in the + * strict (first) round; the relaxed (second) round applies only a + * vcpu->preempted check. + */ +static bool kvm_vcpu_is_good_yield_candidate(struct kvm_vcpu *me, + struct kvm_vcpu *vcpu, + bool yield_to_kernel_mode) +{ + /* Priority 1: confirmed recent IPI receiver. */ + if (kvm_vcpu_is_ipi_receiver(me, vcpu)) + return true; + + /* Priority 2: arch-specific pending-interrupt hint. */ + if (kvm_arch_dy_has_pending_interrupt(vcpu)) + return true; + + /* Priority 3: preempted, with optional in-kernel requirement. */ + if (!READ_ONCE(vcpu->preempted)) + return false; + + if (yield_to_kernel_mode && !kvm_arch_vcpu_preempted_in_kernel(vcpu)) + return false; + + return true; +} + void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) { int nr_vcpus, start, i, idx, yielded; struct kvm *kvm = me->kvm; struct kvm_vcpu *vcpu; int try = 3; + bool first_round = true; nr_vcpus = atomic_read(&kvm->online_vcpus); if (nr_vcpus < 2) @@ -4010,16 +4049,21 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) if (kvm_vcpu_is_blocking(vcpu) && !vcpu_dy_runnable(vcpu)) continue; - /* - * Treat the target vCPU as being in-kernel if it has a pending - * interrupt, as the vCPU trying to yield may be spinning - * waiting on IPI delivery, i.e. the target vCPU is in-kernel - * for the purposes of directed yield. - */ - if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode && - !kvm_arch_dy_has_pending_interrupt(vcpu) && - !kvm_arch_vcpu_preempted_in_kernel(vcpu)) - continue; + if (first_round) { + /* Strict round: IPI-aware and legacy preempted filters. */ + if (!kvm_vcpu_is_good_yield_candidate(me, vcpu, + yield_to_kernel_mode)) + continue; + } else { + /* + * Relaxed round: only require preempted. This is the + * safety net for missed IPI tracking (e.g. APICv) or + * transient runnable-set changes since the strict + * scan. + */ + if (!READ_ONCE(vcpu->preempted)) + continue; + } if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) continue; @@ -4032,6 +4076,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) break; } } + kvm_vcpu_set_in_spin_loop(me, false); /* Ensure vcpu is not eligible during next spinloop */ -- 2.43.0