From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3] IO: Intelligent device lookup on bus Date: Wed, 27 Jul 2011 14:35:51 +0300 Message-ID: <4E2FF817.2090601@redhat.com> References: <1311488156-21998-1-git-send-email-levinsasha928@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Marcelo Tosatti To: Sasha Levin Return-path: Received: from mx1.redhat.com ([209.132.183.28]:13519 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752382Ab1G0Lf4 (ORCPT ); Wed, 27 Jul 2011 07:35:56 -0400 In-Reply-To: <1311488156-21998-1-git-send-email-levinsasha928@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 07/24/2011 09:15 AM, 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. > > Performance test was conducted by comparing exit count per second with > 200 ioeventfds created on one byte and the guest is trying to access a > different byte continuously (triggering usermode exits). > Before the patch the guest has achieved 259k exits per second, after the > patch the guest does 274k exits per second. > > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c > index efad723..094e057 100644 > --- a/arch/x86/kvm/i8254.c > +++ b/arch/x86/kvm/i8254.c > @@ -713,14 +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); Long line. > > -static inline struct kvm_pic *to_pic(struct kvm_io_device *dev) > +static inline struct kvm_pic *to_pic(struct kvm_io_device *dev, gpa_t addr) > { > - return container_of(dev, struct kvm_pic, dev); > + switch (addr) { > + case 0x20: > + case 0x21: > + return container_of(dev, struct kvm_pic, dev_master); > + case 0xa0: > + case 0xa1: > + return container_of(dev, struct kvm_pic, dev_slave); > + case 0x4d0: > + case 0x4d1: > + return container_of(dev, struct kvm_pic, dev_eclr); > + } > + > + return NULL; > } Somewhat ugly. I think int picdev_write_master(...) { return pcidev_write(container_of(...), ...); } is nicer, no? > @@ -560,16 +572,36 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm) > /* > * Initialize PIO device > */ > - kvm_iodevice_init(&s->dev,&picdev_ops); > + kvm_iodevice_init(&s->dev_master,&picdev_ops); > + kvm_iodevice_init(&s->dev_slave,&picdev_ops); > + kvm_iodevice_init(&s->dev_eclr,&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_master); > + if (ret< 0) > + goto fail_unlock; > + > + ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0xa0, 2,&s->dev_slave); > + if (ret< 0) > + goto fail_unlock; > + > + ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0x4d0, 2,&s->dev_eclr); > + if (ret< 0) > + goto fail_unlock; > + > mutex_unlock(&kvm->slots_lock); > - if (ret< 0) { > - kfree(s); > - return NULL; > - } > > return s; > + > +fail_unlock: > + > + mutex_unlock(&kvm->slots_lock); > + kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,&s->dev_master); > + kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,&s->dev_slave); > + kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,&s->dev_eclr); > + > + kfree(s); > + > + return NULL; > } You're unregistering devices that were never registered. It may work now, but it's fragile. > if (ret< 0) > goto out_free_dev; > list_add_tail(&dev->list,&kvm->coalesced_zones); > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 73358d2..f59c1e8 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -586,7 +586,8 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > > kvm_iodevice_init(&p->dev,&ioeventfd_ops); > > - ret = kvm_io_bus_register_dev(kvm, bus_idx,&p->dev); > + ret = kvm_io_bus_register_dev(kvm, bus_idx, p->addr, p->length, > + &p->dev); Should this be p->length or 1? > #include > #include > @@ -2391,24 +2393,94 @@ static void kvm_io_bus_destroy(struct kvm_io_bus *bus) > int i; > > for (i = 0; i< bus->dev_count; i++) { > - struct kvm_io_device *pos = bus->devs[i]; > + struct kvm_io_device *pos = bus->range[i].dev; > This will call the destructor three times for the PIC. Is this safe? -- error compiling committee.c: too many arguments to function