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[Qemu-devel] [PATCH] virtio-pci: Disable virtio-ioeventfd when !CONFIG_I
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD |
Date: |
Tue, 25 Jan 2011 13:58:08 +0000 |
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 <address@hidden>
---
hw/virtio-pci.c | 21 ++++++++++++++++++++-
1 files changed, 20 insertions(+), 1 deletions(-)
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index d07ff97..e921eda 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -640,6 +640,25 @@ static int virtio_pci_set_host_notifier(void *opaque, int
n, bool assign)
return virtio_pci_set_host_notifier_internal(proxy, n, assign);
}
+static bool virtio_pci_can_use_ioeventfd(void)
+{
+ if (!kvm_has_many_ioeventfds()) {
+ return false;
+ }
+
+ /* Use ioeventfd for virtqueue kick only if we have an I/O thread to
+ * perform out-of-line processing. Otherwise we might as well do
+ * synchronous virtqueue kicks and in fact we have to since eventfd does
+ * not support SIGIO. Without the I/O thread a signal would be required to
+ * kick the vcpu out of guest code.
+ */
+#ifdef CONFIG_IOTHREAD
+ return true;
+#else
+ return false;
+#endif
+}
+
static void virtio_pci_vmstate_change(void *opaque, bool running)
{
VirtIOPCIProxy *proxy = opaque;
@@ -705,7 +724,7 @@ static void virtio_init_pci(VirtIOPCIProxy *proxy,
VirtIODevice *vdev,
pci_register_bar(&proxy->pci_dev, 0, size, PCI_BASE_ADDRESS_SPACE_IO,
virtio_map);
- if (!kvm_has_many_ioeventfds()) {
+ if (!virtio_pci_can_use_ioeventfd()) {
proxy->flags &= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD;
}
--
1.7.2.3
- [Qemu-devel] [PATCH] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD,
Stefan Hajnoczi <=