From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] IO: Intelligent device lookup on bus Date: Wed, 20 Jul 2011 14:43:18 +0200 Message-ID: <4E26CD66.1080407@siemens.com> References: <1311163918-14334-1-git-send-email-levinsasha928@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Avi Kivity , Marcelo Tosatti To: Sasha Levin Return-path: Received: from david.siemens.de ([192.35.17.14]:25020 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751309Ab1GTMnX (ORCPT ); Wed, 20 Jul 2011 08:43:23 -0400 In-Reply-To: <1311163918-14334-1-git-send-email-levinsasha928@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2011-07-20 14:11, Sasha Levin wrote: > Currently the method of dealing with an IO operation on a bus (PIO/MMIO) > is to call the read or write callback for each device registered > on the bus until we find a device which handles it. > > Since the number of devices on a bus can be significant due to ioeventfds > and coalesced MMIO zones, this leads to a lot of overhead on each IO > operation. > > Instead of registering devices, we now register ranges which points to > a device. Lookup is done using an efficient bsearch instead of a linear > search. > > This should speed up all IO operations generated by the guest. > > Cc: Avi Kivity > Cc: Marcelo Tosatti > Signed-off-by: Sasha Levin > --- > > This patch depends on '[PATCH v3] MMIO: Make coalesced mmio use a device > per zone'. > > arch/x86/kvm/i8254.c | 4 +- > arch/x86/kvm/i8259.c | 4 +- > include/linux/kvm_host.h | 18 ++++---- > virt/kvm/coalesced_mmio.c | 6 +-- > virt/kvm/eventfd.c | 3 +- > virt/kvm/ioapic.c | 13 +----- > virt/kvm/kvm_main.c | 107 +++++++++++++++++++++++++++++++++++++++----- > 7 files changed, 115 insertions(+), 40 deletions(-) > > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c > index efad723..61d193c 100644 > --- a/arch/x86/kvm/i8254.c > +++ b/arch/x86/kvm/i8254.c > @@ -713,13 +713,15 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags) > kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier); > > kvm_iodevice_init(&pit->dev, &pit_dev_ops); > - ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, &pit->dev); > + ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, KVM_PIT_BASE_ADDRESS, > + KVM_PIT_MEM_LENGTH, &pit->dev); > if (ret < 0) > goto fail; > > if (flags & KVM_PIT_SPEAKER_DUMMY) { > kvm_iodevice_init(&pit->speaker_dev, &speaker_dev_ops); > ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, > + KVM_SPEAKER_BASE_ADDRESS, 4, > &pit->speaker_dev); > if (ret < 0) > goto fail_unregister; > diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c > index 19fe855..c2295af 100644 > --- a/arch/x86/kvm/i8259.c > +++ b/arch/x86/kvm/i8259.c > @@ -562,7 +562,9 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm) > */ > kvm_iodevice_init(&s->dev, &picdev_ops); > mutex_lock(&kvm->slots_lock); > - ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, &s->dev); > + ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0x20, 2, &s->dev); > + ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0xa0, 2, &s->dev); > + ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0x4d0, 2, &s->dev); This made me wonder if you are incorrectly registering the same device multiple times. kvm_io_bus_register_dev is no longer optimally describing what is done here: the registration of an IO range with the bus. And that range is handled by a specific device. Conceptually, a device is only attached once to some bus. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux