From nobody Wed Oct 29 12:14:21 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=quarantine dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1755187718; cv=none; d=zohomail.com; s=zohoarc; b=UxN2702cOxK4foTfseDtIlo4iSZh2JahitHzRrTIUfuK50b/nqpZdNZiwD5DiP8aAXA/bhIYdxuR1zaGpeftbTQQJIAo2GJVNdaHcW1OgiWbH9YOV/kZHwInRWSkYTk6jPHwgAhIv4r2v8JLO/twNG0mM9PCsRz3/cZF/wYA68Y= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1755187718; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=1VVuTG6HLe6NnLPADyzf+X8klPPHgKjfBnNfYtgdoJI=; b=HqfZGJVjOuOBQQ1cbKmSyp8qmpC/3GgZmVOPzs24TXRYPXiymX1D3bdf2hfo3a4hFFp8qQVoKs028i6PY/2NZ3JpiDU9LE9re15aFfutKIUHkvQl5N+ImP5qvqcb0xSLxysOUFun9tYuwz1+bPuBXbQ3PXDGwqmSTfCECIzPXxc= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass header.from= (p=quarantine dis=none) Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1755187718230877.4094936746167; Thu, 14 Aug 2025 09:08:38 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1umaTR-0001lA-Af; Thu, 14 Aug 2025 12:06:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1umaTN-0001kv-VP for qemu-devel@nongnu.org; Thu, 14 Aug 2025 12:06:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1umaTL-0005lQ-Vx for qemu-devel@nongnu.org; Thu, 14 Aug 2025 12:06:37 -0400 Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-315-D4XkgNxCPqedkWjlYvXKCg-1; Thu, 14 Aug 2025 12:06:33 -0400 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8025C1800289 for ; Thu, 14 Aug 2025 16:06:32 +0000 (UTC) Received: from dell-r430-03.lab.eng.brq2.redhat.com (dell-r430-03.lab.eng.brq2.redhat.com [10.37.153.18]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B297A180044F; Thu, 14 Aug 2025 16:06:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755187594; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1VVuTG6HLe6NnLPADyzf+X8klPPHgKjfBnNfYtgdoJI=; b=GtXu5ryL9OViIMkSirTn/4mZS2mA9fEH9HuGw9ohSoo6F7G8ameZKMg0kB2Sfrkh5/wp53 EcTPU9FHVJB6CLnAMwxkRVxnc4SGOCFeJDTS6quAocaZh39+c/2/UOATcbaGsr7yBAYXVN utaaeIwFBBpvGx6sSHcGgHYs3p/ropM= X-MC-Unique: D4XkgNxCPqedkWjlYvXKCg-1 X-Mimecast-MFC-AGG-ID: D4XkgNxCPqedkWjlYvXKCg_1755187592 From: Igor Mammedov To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Peter Xu , "Michael S. Tsirkin" , mtosatti@redhat.com Subject: [PATCH v4 7/8] kvm: i386: irqchip: take BQL only if there is an interrupt Date: Thu, 14 Aug 2025 18:05:59 +0200 Message-ID: <20250814160600.2327672-8-imammedo@redhat.com> In-Reply-To: <20250814160600.2327672-1-imammedo@redhat.com> References: <20250814160600.2327672-1-imammedo@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1755187720469116600 when kernel-irqchip=3Dsplit is used, QEMU still hits BQL contention issue when reading ACPI PM/HPET timers (despite of timer[s] access being lock-less). So Windows with more than 255 cpus is still not able to boot (since it requires iommu -> split irqchip). Problematic path is in kvm_arch_pre_run() where BQL is taken unconditionally when split irqchip is in use. There are a few parts that BQL protects there: 1. interrupt check and injecting however we do not take BQL when checking for pending interrupt (even within the same function), so the patch takes the same approach for cpu->interrupt_request checks and takes BQL only if there is a job to do. 2. request_interrupt_window access CPUState::kvm_run::request_interrupt_window doesn't need BQL as it's accessed by its own vCPU thread. 3. cr8/cpu_get_apic_tpr access the same (as #2) applies to CPUState::kvm_run::cr8, and APIC registers are also cached/synced (get/put) within the vCPU thread it belongs to. Taking BQL only when is necessary, eleminates BQL bottleneck on IO/MMIO only exit path, improoving latency by 80% on HPET micro benchmark. This lets Windows to boot succesfully (in case hv-time isn't used) when more than 255 vCPUs are in use. Signed-off-by: Igor Mammedov Reviewed-by: Peter Xu --- v3: * drop net needed pair of () in cpu->interrupt_request & CPU_INTERRUPT_HA= RD check * Paolo Bonzini * don't take BQL when setting exit_request, use qatomic_set() instead * after above simplification take/release BQL unconditionally * drop smp_mb() after run->cr8/run->request_interrupt_window update --- target/i386/kvm/kvm.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index a7b5c8f81b..306430a052 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -5478,9 +5478,6 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *= run) } } =20 - if (!kvm_pic_in_kernel()) { - bql_lock(); - } =20 /* Force the VCPU out of its inner loop to process any INIT requests * or (for userspace APIC, but it is cheap to combine the checks here) @@ -5489,10 +5486,10 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run= *run) if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) { if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT) && !(env->hflags & HF_SMM_MASK)) { - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, 1); } if (cpu_test_interrupt(cpu, CPU_INTERRUPT_TPR)) { - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, 1); } } =20 @@ -5503,6 +5500,8 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *= run) (env->eflags & IF_MASK)) { int irq; =20 + bql_lock(); + cpu->interrupt_request &=3D ~CPU_INTERRUPT_HARD; irq =3D cpu_get_pic_interrupt(env); if (irq >=3D 0) { @@ -5517,6 +5516,7 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *= run) strerror(-ret)); } } + bql_unlock(); } =20 /* If we have an interrupt but the guest is not ready to receive an @@ -5531,8 +5531,6 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *= run) =20 DPRINTF("setting tpr\n"); run->cr8 =3D cpu_get_apic_tpr(x86_cpu->apic_state); - - bql_unlock(); } } =20 --=20 2.47.1