From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [Qemu-devel] [PATCH 1/2] return available ioeventfds count in kvm_has_many_ioeventfds() Date: Tue, 13 Mar 2012 13:24:40 +0100 Message-ID: <4F5F3C88.9000707@siemens.com> References: <20120313103602.8741.71939.stgit@dhcp-8-167.nay.redhat.com> <20120313104232.8741.89133.stgit@dhcp-8-167.nay.redhat.com> <4F5F34A2.6070301@siemens.com> <4F5F36D8.9050800@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: "aliguori@us.ibm.com" , "stefanha@linux.vnet.ibm.com" , "kvm@vger.kernel.org" , "mtosatti@redhat.com" , "qemu-devel@nongnu.org" , "avi@redhat.com" To: Amos Kong Return-path: Received: from goliath.siemens.de ([192.35.17.28]:20608 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751022Ab2CMMY4 (ORCPT ); Tue, 13 Mar 2012 08:24:56 -0400 In-Reply-To: <4F5F36D8.9050800@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2012-03-13 13:00, Amos Kong wrote: > On 13/03/12 19:50, Jan Kiszka wrote: >> Please tag uq/master patches with "PATCH uq/master". >> >> On 2012-03-13 11:42, Amos Kong wrote: >>> Older kernels have a 6 device limit on the KVM io bus. >>> This patch makes kvm_has_many_ioeventfds() return available >>> ioeventfd count. ioeventfd will be disabled if there is >>> no 7 available ioeventfds. >>> >>> Signed-off-by: Amos Kong >>> --- >>> hw/virtio-pci.c | 2 +- >>> kvm-all.c | 9 +++------ >>> 2 files changed, 4 insertions(+), 7 deletions(-) >>> >>> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c >>> index a0fb7c1..d63f303 100644 >>> --- a/hw/virtio-pci.c >>> +++ b/hw/virtio-pci.c >>> @@ -678,7 +678,7 @@ void virtio_init_pci(VirtIOPCIProxy *proxy, VirtIODevice *vdev) >>> pci_register_bar(&proxy->pci_dev, 0, PCI_BASE_ADDRESS_SPACE_IO, >>> &proxy->bar); >>> >>> - if (!kvm_has_many_ioeventfds()) { >>> + if (kvm_has_many_ioeventfds() != 7) { >>> proxy->flags&= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD; >>> } >>> >>> diff --git a/kvm-all.c b/kvm-all.c >>> index 3c6b4f0..d12694b 100644 >>> --- a/kvm-all.c >>> +++ b/kvm-all.c >>> @@ -78,7 +78,6 @@ struct KVMState >>> int pit_in_kernel; >>> int pit_state2; >>> int xsave, xcrs; >>> - int many_ioeventfds; >>> int irqchip_inject_ioctl; >>> #ifdef KVM_CAP_IRQ_ROUTING >>> struct kvm_irq_routing *irq_routes; >>> @@ -510,8 +509,8 @@ static int kvm_check_many_ioeventfds(void) >>> } >>> } >>> >>> - /* Decide whether many devices are supported or not */ >>> - ret = i == ARRAY_SIZE(ioeventfds); >>> + /* If i equals to 7, many devices are supported */ >>> + ret = i; >>> >>> while (i--> 0) { >>> kvm_set_ioeventfd_pio_word(ioeventfds[i], 0, i, false); >>> @@ -1078,8 +1077,6 @@ int kvm_init(void) >>> kvm_state = s; >>> memory_listener_register(&kvm_memory_listener, NULL); >>> >>> - s->many_ioeventfds = kvm_check_many_ioeventfds(); >>> - >>> cpu_interrupt_handler = kvm_handle_interrupt; >>> >>> return 0; >>> @@ -1407,7 +1404,7 @@ int kvm_has_many_ioeventfds(void) >>> if (!kvm_enabled()) { >>> return 0; >>> } >>> - return kvm_state->many_ioeventfds; >>> + return kvm_check_many_ioeventfds(); >> >> And why are you dropping the caching of the kvm_check_many_ioeventfds() >> return value? Is kvm_has_many_ioeventfds not used outside init scopes? > > Hi Jan, > > In the past, kvm_state->many_ioeventfds is only updated once at the > beginning, And the additional use case of patch 2 is not hot path either, right? > I want to use kvm_check_many_ioeventfds() to check if available > ioeventfd exists > before starting ioeventfd each time. OK, but than kvm_has_many_ioeventfds is not the right name for this function anymore. Call it "kvm_get_available_ioventfds" or so, but not in a away that implies a boolean return value. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux