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([175.170.92.22]) by smtp.googlemail.com with ESMTPSA id d9443c01a7336-2a2f3d4d36esm7368135ad.63.2025.12.18.19.54.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Dec 2025 19:54:06 -0800 (PST) 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 Subject: [PATCH v2 7/9] KVM: x86/lapic: Integrate IPI tracking with interrupt delivery Date: Fri, 19 Dec 2025 11:53:31 +0800 Message-ID: <20251219035334.39790-8-kernellwp@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251219035334.39790-1-kernellwp@gmail.com> References: <20251219035334.39790-1-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 Hook IPI tracking into the LAPIC interrupt delivery path to capture sender/receiver relationships for directed yield optimization. Implement kvm_ipi_track_send() called from kvm_irq_delivery_to_apic() when a unicast fixed IPI is detected (exactly one destination). Record sender vCPU index, receiver vCPU index, and timestamp using lockless WRITE_ONCE for minimal overhead. Implement kvm_ipi_track_eoi() called from kvm_apic_set_eoi_accelerated() and handle_apic_eoi() to clear IPI context when interrupts are acknowledged. Use two-stage clearing: 1. Unconditionally clear the receiver's context (it processed the IPI) 2. Conditionally clear sender's pending flag only when the sender exists, last_ipi_receiver matches, and the IPI is recent Use lockless accessors for minimal overhead. The tracking only activates for unicast fixed IPIs where directed yield provides value. Signed-off-by: Wanpeng Li --- arch/x86/kvm/lapic.c | 90 ++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 86 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 23f247a3b127..d4fb6f49390b 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1270,6 +1270,9 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src, struct kvm_lapic **dst = NULL; int i; bool ret; + int targets = 0; + int delivered; + struct kvm_vcpu *unique = NULL; *r = -1; @@ -1291,8 +1294,22 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src, for_each_set_bit(i, &bitmap, 16) { if (!dst[i]) continue; - *r += kvm_apic_set_irq(dst[i]->vcpu, irq, dest_map); + delivered = kvm_apic_set_irq(dst[i]->vcpu, irq, dest_map); + *r += delivered; + if (delivered > 0) { + targets++; + unique = dst[i]->vcpu; + } } + + /* + * Track IPI for directed yield: only for LAPIC-originated + * APIC_DM_FIXED without shorthand, with exactly one recipient. + */ + if (src && irq->delivery_mode == APIC_DM_FIXED && + irq->shorthand == APIC_DEST_NOSHORT && + targets == 1 && unique && unique != src->vcpu) + kvm_track_ipi_communication(src->vcpu, unique); } rcu_read_unlock(); @@ -1377,6 +1394,9 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src, struct kvm_vcpu *vcpu, *lowest = NULL; unsigned long i, dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)]; unsigned int dest_vcpus = 0; + int targets = 0; + int delivered; + struct kvm_vcpu *unique = NULL; if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map)) return r; @@ -1400,7 +1420,12 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src, if (!kvm_lowest_prio_delivery(irq)) { if (r < 0) r = 0; - r += kvm_apic_set_irq(vcpu, irq, dest_map); + delivered = kvm_apic_set_irq(vcpu, irq, dest_map); + r += delivered; + if (delivered > 0) { + targets++; + unique = vcpu; + } } else if (kvm_apic_sw_enabled(vcpu->arch.apic)) { if (!vector_hashing_enabled) { if (!lowest) @@ -1421,8 +1446,23 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src, lowest = kvm_get_vcpu(kvm, idx); } - if (lowest) - r = kvm_apic_set_irq(lowest, irq, dest_map); + if (lowest) { + delivered = kvm_apic_set_irq(lowest, irq, dest_map); + r = delivered; + if (delivered > 0) { + targets = 1; + unique = lowest; + } + } + + /* + * Track IPI for directed yield: only for LAPIC-originated + * APIC_DM_FIXED without shorthand, with exactly one recipient. + */ + if (src && irq->delivery_mode == APIC_DM_FIXED && + irq->shorthand == APIC_DEST_NOSHORT && + targets == 1 && unique && unique != src->vcpu) + kvm_track_ipi_communication(src->vcpu, unique); return r; } @@ -1608,6 +1648,45 @@ static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector) #endif } +/* + * Clear IPI context on EOI to prevent stale boost decisions. + * + * Two-stage cleanup: + * 1. Always clear receiver's IPI context (it processed the interrupt) + * 2. Conditionally clear sender's pending flag only when: + * - Sender vCPU exists and is valid + * - Sender's last_ipi_receiver matches this receiver + * - IPI was sent recently (within window) + */ +static void kvm_clear_ipi_on_eoi(struct kvm_lapic *apic) +{ + struct kvm_vcpu *receiver = apic->vcpu; + int sender_idx; + u64 then, now; + + if (unlikely(!READ_ONCE(ipi_tracking_enabled))) + return; + + sender_idx = READ_ONCE(receiver->arch.ipi_context.last_ipi_sender); + + /* Step 1: Always clear receiver's IPI context */ + kvm_vcpu_clear_ipi_context(receiver); + + /* Step 2: Conditionally clear sender's pending flag */ + if (sender_idx >= 0) { + struct kvm_vcpu *sender = kvm_get_vcpu(receiver->kvm, sender_idx); + + if (sender && + READ_ONCE(sender->arch.ipi_context.last_ipi_receiver) == + receiver->vcpu_idx) { + then = READ_ONCE(sender->arch.ipi_context.ipi_time_ns); + now = ktime_get_mono_fast_ns(); + if (now - then <= ipi_window_ns) + WRITE_ONCE(sender->arch.ipi_context.pending_ipi, false); + } + } +} + static int apic_set_eoi(struct kvm_lapic *apic) { int vector = apic_find_highest_isr(apic); @@ -1643,6 +1722,7 @@ void kvm_apic_set_eoi_accelerated(struct kvm_vcpu *vcpu, int vector) trace_kvm_eoi(apic, vector); kvm_ioapic_send_eoi(apic, vector); + kvm_clear_ipi_on_eoi(apic); kvm_make_request(KVM_REQ_EVENT, apic->vcpu); } EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_apic_set_eoi_accelerated); @@ -2453,6 +2533,8 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val) case APIC_EOI: apic_set_eoi(apic); + /* Precise cleanup for IPI-aware boost */ + kvm_clear_ipi_on_eoi(apic); break; case APIC_LDR: -- 2.43.0