From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=42899 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PjvfY-0002as-Ss for qemu-devel@nongnu.org; Mon, 31 Jan 2011 10:27:59 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PjvfP-0003Pj-Mr for qemu-devel@nongnu.org; Mon, 31 Jan 2011 10:27:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:61341) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PjvfP-0003Pd-Fw for qemu-devel@nongnu.org; Mon, 31 Jan 2011 10:27:47 -0500 From: Kevin Wolf Date: Mon, 31 Jan 2011 16:28:56 +0100 Message-Id: <1296487756-12553-9-git-send-email-kwolf@redhat.com> In-Reply-To: <1296487756-12553-1-git-send-email-kwolf@redhat.com> References: <1296487756-12553-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH 08/28] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws Cc: kwolf@redhat.com, qemu-devel@nongnu.org From: Stefan Hajnoczi It is not possible to use virtio-ioeventfd when building without an I/O thread. We rely on a signal to kick us out of vcpu execution. Timers and AIO use SIGALRM and SIGUSR2 respectively. Unfortunately eventfd does not support O_ASYNC (SIGIO) so eventfd cannot be used in a signal driven manner. Signed-off-by: Stefan Hajnoczi Acked-by: Michael S. Tsirkin Signed-off-by: Kevin Wolf --- kvm-all.c | 8 ++++++-- 1 files changed, 6 insertions(+), 2 deletions(-) diff --git a/kvm-all.c b/kvm-all.c index 255b6fa..8f0e17c 100644 --- a/kvm-all.c +++ b/kvm-all.c @@ -449,10 +449,14 @@ int kvm_check_extension(KVMState *s, unsigned int extension) static int kvm_check_many_ioeventfds(void) { - /* Older kernels have a 6 device limit on the KVM io bus. Find out so we + /* Userspace can use ioeventfd for io notification. This requires a host + * that supports eventfd(2) and an I/O thread; since eventfd does not + * support SIGIO it cannot interrupt the vcpu. + * + * Older kernels have a 6 device limit on the KVM io bus. Find out so we * can avoid creating too many ioeventfds. */ -#ifdef CONFIG_EVENTFD +#if defined(CONFIG_EVENTFD) && defined(CONFIG_IOTHREAD) int ioeventfds[7]; int i, ret = 0; for (i = 0; i < ARRAY_SIZE(ioeventfds); i++) { -- 1.7.2.3