netdev - Re: [PATCH v2 2/5] VSOCK: support fill data to mergeable rx buffer in host

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Date:   Thu, 13 Dec 2018 09:50:28 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     jiangyiwen <jiangyiwen@...wei.com>
Cc:     David Miller <davem@...emloft.net>, stefanha@...hat.com,
        jasowang@...hat.com, netdev@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 2/5] VSOCK: support fill data to mergeable rx buffer
 in host

On Thu, Dec 13, 2018 at 11:11:48AM +0800, jiangyiwen wrote:
> On 2018/12/13 3:09, David Miller wrote:
> > From: jiangyiwen <jiangyiwen@...wei.com>
> > Date: Wed, 12 Dec 2018 17:29:31 +0800
> > 
> >> diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
> >> index 1d57ed3..2292f30 100644
> >> --- a/include/uapi/linux/virtio_vsock.h
> >> +++ b/include/uapi/linux/virtio_vsock.h
> >> @@ -63,6 +63,11 @@ struct virtio_vsock_hdr {
> >>  	__le32	fwd_cnt;
> >>  } __attribute__((packed));
> >>
> >> +/* It add mergeable rx buffers feature */
> >> +struct virtio_vsock_mrg_rxbuf_hdr {
> >> +	__le16  num_buffers;    /* number of mergeable rx buffers */
> >> +} __attribute__((packed));
> >> +
> > 
> > I know the rest of this file uses 'packed' but this attribute should
> > only be used if absolutely necessary as it incurs a
> > non-trivial performance penalty for some architectures.
> > 
> > .
> > 
> 
> Hi David,
> 
> I hope Host can fill fewer bytes into rx virtqueue, so
> I keep structure virtio_vsock_mrg_rxbuf_hdr one byte
> alignment.
> 
> Thanks,
> Yiwen.

It doesn't work like this now though, does it?
Buffers are preallocated and they are always aligned.
So I do not see the point.

-- 
MST