From nobody Sun Feb 8 21:26:51 2026 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3BB443148B7 for ; Tue, 9 Sep 2025 10:00:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757412021; cv=none; b=oSLmiNIW5Z0uxyDFA4WJMf2S/1yAHqwhaGKSnla+y2Y/5BmgpySckbhnXcJBkP5CEzVFlI2rGADZPFrzveFbD6KYkjcSsgTsa2LfmNPoX7Z2CYVPX2T0EWJ+ZTlKtPbsDYX3KyfZVuwEdDgZzPZBKavCiuOSbAEOBJpHC2mLh2c= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757412021; c=relaxed/simple; bh=TC0/DAtjo962c3w2zSDYnWaaPOAlIjdtxO5AuA4+e2w=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Z90Dr398Kt2BxVzWYAGgjsrGKzjGW0tie5PCsQrvgiPa2X0rqa1q5ZoJBQKL3TxZxmVvjtcR8DeE9M4KqjCPTbczF3Mbgyz7nGAZcBjdSNLD0+VKtbid+KT6Y2b0W3sGrmLRzaYNd8e7igiOOEzJlBb8jkR1IGBl3p1un8WHkdc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--keirf.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=1GmjjfUw; arc=none smtp.client-ip=209.85.128.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--keirf.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="1GmjjfUw" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-45cb6d8f42bso52074875e9.2 for ; Tue, 09 Sep 2025 03:00:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1757412017; x=1758016817; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=4CHS3L1HTq4zc8VOJcXLjTfuiOI6XTDNN7808wd2BIw=; b=1GmjjfUwiiUwu3JdR8EZJP5otoGKdB03MG6c4El4E8aHUNetf6oIhlZWG/1hz7Gp1/ 72P0bflVoELsFQCB7Xb6fiPhN4xC8jMqYOPsOHEc3UW2ShY6RFU41Pn9Dj6BhN3YSMKM btDTwxSNZDI1QV53Au+v8mxrlyffgblqOZiWiKrLkkDnONsMSQmTUmdrcAgORdNPhNRB fZlKn7YlIEn5F88kVxe81fQTcI+uCuwVByZzmY6raeAsQuUU9OHPChAowMZLVWtPO4Zx 6Ho4NAOcfv8PW5uKfuGUEyGSlv38UIhUKUPfgJyfoyOpLRQ61kaiJjL/m0SPMPFq7PLg KHEQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757412017; x=1758016817; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=4CHS3L1HTq4zc8VOJcXLjTfuiOI6XTDNN7808wd2BIw=; b=labj3DUkYQsczQfcPJHdw+K40WySwhlL2FZHOvbcgsAtAQQo6liDKNfKY5xt8Nafxg 6Go8mQMeVqVmKf+PvrSK+ACEpEE+qFeIyXY6k2FxVgpvxincCQzqWhopnaBkoD/BcZHn ibiHsl7wsYw7acihpGjTvflqxBv4mUZL/0PykLQI1G1vlB5mng0tB30cBQjHV3qLKpEm BXvykv0qrAk3OxboEzCORc5pdUlF3yypQSv6ObbgeromxDArL6zFHkXJ/HRCdkClWGlq 8QDoOc3k2qnMt/QbA53AZluDPpRBiONN6UTvEKWsC4YJJ8yUujzMD/+1tYmfC5Vgytq+ Qxvw== X-Forwarded-Encrypted: i=1; AJvYcCVfYOBLtZvw1D5osSYFGL1adesCf6JGKwq3vYXeCqxAEDqSi4rWUyLGgNouj6PrOfos/7FT6BFRrjdLmKo=@vger.kernel.org X-Gm-Message-State: AOJu0Yx+4e9upxdhBed0xfqigIN6gUk4WfayUhLI/xHDGQsUXrYqyvrw ljD/7s2x/xLjWT0U/kYoB+bMhp2gH5RbZLOVly0wD5zkd1rDhCyR+3zWxLNg2wosNAOl8jBDvT9 GDQ== X-Google-Smtp-Source: AGHT+IFFKS9LSCg4pqICkObMpdq7WwENyXMbo01qMECVjQhfTtItSGy3G3y/UQTpd1+00goRvADrbyzv2A== X-Received: from wmbei14.prod.google.com ([2002:a05:600c:3f0e:b0:45d:e45e:96aa]) (user=keirf job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:548a:b0:458:bfb1:1fb6 with SMTP id 5b1f17b1804b1-45ddde6a471mr83472825e9.2.1757412017523; Tue, 09 Sep 2025 03:00:17 -0700 (PDT) Date: Tue, 9 Sep 2025 10:00:07 +0000 In-Reply-To: <20250909100007.3136249-1-keirf@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250909100007.3136249-1-keirf@google.com> X-Mailer: git-send-email 2.51.0.384.g4c02a37b29-goog Message-ID: <20250909100007.3136249-5-keirf@google.com> Subject: [PATCH v4 4/4] KVM: Avoid synchronize_srcu() in kvm_io_bus_register_dev() From: Keir Fraser To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Eric Auger , Oliver Upton , Marc Zyngier , Will Deacon , Paolo Bonzini , Keir Fraser , Li RongQing Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Device MMIO registration may happen quite frequently during VM boot, and the SRCU synchronization each time has a measurable effect on VM startup time. In our experiments it can account for around 25% of a VM's startup time. Replace the synchronization with a deferred free of the old kvm_io_bus structure. Tested-by: Li RongQing Signed-off-by: Keir Fraser --- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index e7d6111cf254..103be35caf0d 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -206,6 +206,7 @@ struct kvm_io_range { struct kvm_io_bus { int dev_count; int ioeventfd_count; + struct rcu_head rcu; struct kvm_io_range range[]; }; =20 diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 870ad8ea93a7..bcef324ccbf2 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1320,6 +1320,7 @@ static void kvm_destroy_vm(struct kvm *kvm) kvm_free_memslots(kvm, &kvm->__memslots[i][1]); } cleanup_srcu_struct(&kvm->irq_srcu); + srcu_barrier(&kvm->srcu); cleanup_srcu_struct(&kvm->srcu); #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES xa_destroy(&kvm->mem_attr_array); @@ -5952,6 +5953,13 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_= bus bus_idx, gpa_t addr, } EXPORT_SYMBOL_GPL(kvm_io_bus_read); =20 +static void __free_bus(struct rcu_head *rcu) +{ + struct kvm_io_bus *bus =3D container_of(rcu, struct kvm_io_bus, rcu); + + kfree(bus); +} + int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t a= ddr, int len, struct kvm_io_device *dev) { @@ -5990,8 +5998,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm= _bus bus_idx, gpa_t addr, memcpy(new_bus->range + i + 1, bus->range + i, (bus->dev_count - i) * sizeof(struct kvm_io_range)); rcu_assign_pointer(kvm->buses[bus_idx], new_bus); - synchronize_srcu_expedited(&kvm->srcu); - kfree(bus); + call_srcu(&kvm->srcu, &bus->rcu, __free_bus); =20 return 0; } --=20 2.51.0.384.g4c02a37b29-goog