KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Eli Cohen <eli@mellanox.com>
To: Jason Wang <jasowang@redhat.com>
Cc: Zhu Lingshan <lingshan.zhu@intel.com>,
	alex.williamson@redhat.com, mst@redhat.com, pbonzini@redhat.com,
	sean.j.christopherson@intel.com, wanpengli@tencent.com,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, kvm@vger.kernel.org,
	shahafs@mellanox.com, parav@mellanox.com
Subject: Re: [PATCH V4 4/6] vhost_vdpa: implement IRQ offloading in vhost_vdpa
Date: Wed, 29 Jul 2020 14:13:06 +0300
Message-ID: <20200729111306.GE35280@mtl-vdi-166.wap.labs.mlnx> (raw)
In-Reply-To: <45b7e8aa-47a9-06f6-6b72-762d504adb00@redhat.com>

On Wed, Jul 29, 2020 at 06:19:52PM +0800, Jason Wang wrote:
I am checking internally if we can work in a mode not requiring to
acknowledge the interrupt. I will update.

Thanks for the explanations.

> 
> 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?
> >>>
> 

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28  4:23 [PATCH V4 0/6] IRQ offloading for vDPA Zhu Lingshan
2020-07-28  4:24 ` [PATCH V4 1/6] vhost: introduce vhost_vring_call Zhu Lingshan
2020-07-28  4:24 ` [PATCH V4 2/6] kvm: detect assigned device via irqbypass manager Zhu Lingshan
2020-07-28  4:24 ` [PATCH V4 3/6] vDPA: add get_vq_irq() in vdpa_config_ops Zhu Lingshan
2020-07-28  7:42   ` Jason Wang
2020-07-28  4:24 ` [PATCH V4 4/6] vhost_vdpa: implement IRQ offloading in vhost_vdpa Zhu Lingshan
2020-07-28  7:53   ` Jason Wang
     [not found]     ` <f3e375da-3aa8-7a0c-237c-25943667a535@intel.com>
2020-07-28 10:29       ` Jason Wang
2020-07-28  9:04   ` Eli Cohen
2020-07-29  9:21     ` Jason Wang
2020-07-29  9:55       ` Eli Cohen
2020-07-29 10:19         ` Jason Wang
2020-07-29 11:13           ` Eli Cohen [this message]
2020-07-29 14:15           ` Eli Cohen
2020-07-31  3:11             ` Jason Wang
2020-07-28  4:24 ` [PATCH V4 5/6] ifcvf: implement vdpa_config_ops.get_vq_irq() Zhu Lingshan
2020-07-28  4:24 ` [PATCH V4 6/6] irqbypass: do not start cons/prod when failed connect Zhu Lingshan
2020-07-31  3:18 ` [PATCH V4 0/6] IRQ offloading for vDPA Jason Wang

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200729111306.GE35280@mtl-vdi-166.wap.labs.mlnx \
    --to=eli@mellanox.com \
    --cc=alex.williamson@redhat.com \
    --cc=jasowang@redhat.com \
    --cc=kvm@vger.kernel.org \
    --cc=lingshan.zhu@intel.com \
    --cc=mst@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=parav@mellanox.com \
    --cc=pbonzini@redhat.com \
    --cc=sean.j.christopherson@intel.com \
    --cc=shahafs@mellanox.com \
    --cc=virtualization@lists.linux-foundation.org \
    --cc=wanpengli@tencent.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git