On 2020/7/29 下午5:55, Eli Cohen wrote:
On Wed, Jul 29, 2020 at 05:21:53PM +0800, Jason Wang wrote:
On 2020/7/28 下午5:04, Eli Cohen wrote:
On Tue, Jul 28, 2020 at 12:24:03PM +0800, Zhu Lingshan wrote:
+static void vhost_vdpa_setup_vq_irq(struct vhost_vdpa *v, int qid)
+{
+ struct vhost_virtqueue *vq = &v->vqs[qid];
+ const struct vdpa_config_ops *ops = v->vdpa->config;
+ struct vdpa_device *vdpa = v->vdpa;
+ int ret, irq;
+
+ spin_lock(&vq->call_ctx.ctx_lock);
+ irq = ops->get_vq_irq(vdpa, qid);
+ if (!vq->call_ctx.ctx || irq == -EINVAL) {
+ spin_unlock(&vq->call_ctx.ctx_lock);
+ return;
+ }
+
If I understand correctly, this will cause these IRQs to be forwarded
directly to the VCPU, e.g. will be handled by the guest/qemu.
Yes, if it can bypassed, the interrupt will be delivered to vCPU directly.
So, usually the network driver knows how to handle interrups for its
devices. I assume the virtio_net driver at the guest has some default
processing but what if the underlying hardware device (such as the case
of vdpa) needs to take some actions?
Virtio splits the bus operations out of device operations. So did the
driver.
The virtio-net driver depends on a transport driver to talk to the real
device. Usually PCI is used as the transport for the device. In this
case virtio-pci driver is in charge of dealing with irq
allocation/free/configuration and it needs to co-operate with platform
specific irqchip (virtualized by KVM) to finish the work like irq
acknowledge etc. E.g for x86, the irq offloading can only work when
there's a hardware support of virtual irqchip (APICv) then all stuffs
could be done without vmexits.
So no vendor specific part since the device and transport are all standard.
Is there an option to do bounce the
interrupt back to the vendor specific driver in the host so it can take
these actions?
Currently not, but even if we can do this, I'm afraid we will lose the
performance advantage of irq bypassing.
Does this mean that the host will not handle this interrupt? How does it
work in case on level triggered interrupts?
There's no guarantee that the KVM arch code can make sure the irq
bypass work for any type of irq. So if they the irq will still need
to be handled by host first. This means we should keep the host
interrupt handler as a slowpath (fallback).
In the case of ConnectX, I need to execute some code to acknowledge the
interrupt.
This turns out to be hard for irq bypassing to work. Is it because
the irq is shared or what kind of ack you need to do?
I have an EQ which is a queue for events comming from the hardware. This
EQ can created so it reports only completion events but I still need to
execute code that roughly tells the device that I saw these event
records and then arm it again so it can report more interrupts (e.g if
more packets are received or sent). This is device specific code.
Any chance that the hardware can use MSI (which is not the case here)?
Thanks
Thanks
Can you explain how this should be done?
