* [Qemu-devel] [PATCH v3] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD
@ 2011-01-25 16:17 Stefan Hajnoczi
2011-01-25 17:42 ` [Qemu-devel] " Michael S. Tsirkin
0 siblings, 1 reply; 3+ messages in thread
From: Stefan Hajnoczi @ 2011-01-25 16:17 UTC (permalink / raw)
To: qemu-devel; +Cc: Kevin Wolf, Stefan Hajnoczi, Michael S. Tsirkin
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 <stefanha@linux.vnet.ibm.com>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [Qemu-devel] Re: [PATCH v3] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD
2011-01-25 16:17 [Qemu-devel] [PATCH v3] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD Stefan Hajnoczi
@ 2011-01-25 17:42 ` Michael S. Tsirkin
2011-01-26 10:19 ` Kevin Wolf
0 siblings, 1 reply; 3+ messages in thread
From: Michael S. Tsirkin @ 2011-01-25 17:42 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: Kevin Wolf, qemu-devel
On Tue, Jan 25, 2011 at 04:17:14PM +0000, Stefan Hajnoczi wrote:
> 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 <stefanha@linux.vnet.ibm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] Re: [PATCH v3] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD
2011-01-25 17:42 ` [Qemu-devel] " Michael S. Tsirkin
@ 2011-01-26 10:19 ` Kevin Wolf
0 siblings, 0 replies; 3+ messages in thread
From: Kevin Wolf @ 2011-01-26 10:19 UTC (permalink / raw)
To: Michael S. Tsirkin; +Cc: Stefan Hajnoczi, qemu-devel
Am 25.01.2011 18:42, schrieb Michael S. Tsirkin:
> On Tue, Jan 25, 2011 at 04:17:14PM +0000, Stefan Hajnoczi wrote:
>> 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 <stefanha@linux.vnet.ibm.com>
>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
I guess this means that it should go through my tree? I applied it to
the block branch now.
Kevin
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2011-01-26 10:17 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2011-01-25 16:17 [Qemu-devel] [PATCH v3] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD Stefan Hajnoczi
2011-01-25 17:42 ` [Qemu-devel] " Michael S. Tsirkin
2011-01-26 10:19 ` Kevin Wolf
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