linux-kernel - Re: [PATCH V11 19/19] virtio

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Message-ID: <CACGkMEuH0x1xxC1+yHg3A8hdEz=XMRCnSM9zarEFa=8=BcnsyQ@mail.gmail.com>
Date: Mon, 29 Dec 2025 15:18:08 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com, 
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V11 19/19] virtio_ring: add in order support

On Sat, Dec 27, 2025 at 3:57 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Dec 25, 2025 at 12:26:08PM +0800, Jason Wang wrote:
> > This patch implements in order support for both split virtqueue and
> > packed virtqueue. Performance could be gained for the device where the
> > memory access could be expensive (e.g vhost-net or a real PCI device):
> >
> > Benchmark with KVM guest:
> >
> > Vhost-net on the host: (pktgen + XDP_DROP):
> >
> >          in_order=off | in_order=on | +%
> >     TX:  4.51Mpps     | 5.30Mpps    | +17%
> >     RX:  3.47Mpps     | 3.61Mpps    | + 4%
> >
> > Vhost-user(testpmd) on the host: (pktgen/XDP_DROP):
> >
> > For split virtqueue:
> >
> >          in_order=off | in_order=on | +%
> >     TX:  5.60Mpps     | 5.60Mpps    | +0.0%
> >     RX:  9.16Mpps     | 9.61Mpps    | +4.9%
> >
> > For packed virtqueue:
> >
> >          in_order=off | in_order=on | +%
> >     TX:  5.60Mpps     | 5.70Mpps    | +1.7%
> >     RX:  10.6Mpps     | 10.8Mpps    | +1.8%
> >
> > Benchmark also shows no performance impact for in_order=off for queue
> > size with 256 and 1024.
> >
> > Reviewed-by: Eugenio Pérez <eperezma@...hat.com>
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > ---

[...]

> > +unmap_release:
> > +     err_idx = i;
> > +     i = head;
> > +     vq->packed.avail_used_flags = avail_used_flags;
>
> Hmm. But this does not roll back packed.avail_wrap_counter.
> Shouldn't it?

Fixed.

Thanks