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From: "Wangyunjian(wangyunjian,TongTu)" <wangyunjian@huawei.com>
To: Stephen Hemminger <stephen@networkplumber.org>
CC: "dev@dpdk.org" <dev@dpdk.org>, "maxime.coquelin@redhat.com"
<maxime.coquelin@redhat.com>, "chenbox@nvidia.com" <chenbox@nvidia.com>,
"Lilijun (Jerry)" <jerry.lilijun@huawei.com>, "xiawei (H)"
<xiawei40@huawei.com>, wangzengyuan <wangzengyuan@huawei.com>,
"stable@dpdk.org" <stable@dpdk.org>
Subject: RE: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading
Thread-Topic: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading
Thread-Index: AQHbUeCfDFMb3moSS0+hMQxlUzfoA7Lu0JIAgARTyfA=
Date: Mon, 23 Dec 2024 02:45:48 +0000
Message-ID: <96dbb1599a3943f39c7e80d31dd3881a@huawei.com>
References: <91dc12662805a3867413940f856ba9454b91c579.1734588243.git.wangyunjian@huawei.com>
<20241220083546.4b5ba9c9@hermes.local>
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> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Saturday, December 21, 2024 12:36 AM
> To: Wangyunjian(wangyunjian,TongTu) <wangyunjian@huawei.com>
> Cc: dev@dpdk.org; maxime.coquelin@redhat.com; chenbox@nvidia.com;
> Lilijun (Jerry) <jerry.lilijun@huawei.com>; xiawei (H) <xiawei40@huawei.c=
om>;
> wangzengyuan <wangzengyuan@huawei.com>; stable@dpdk.org
> Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloadin=
g
>=20
> On Thu, 19 Dec 2024 14:38:28 +0800
> Yunjian Wang <wangyunjian@huawei.com> wrote:
>=20
> > diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> > index 69901ab3b5..5c40ae7069 100644
> > --- a/lib/vhost/virtio_net.c
> > +++ b/lib/vhost/virtio_net.c
> > @@ -2914,10 +2914,12 @@ desc_to_mbuf(struct virtio_net *dev, struct
> vhost_virtqueue *vq,
> > * in a contiguous virtual area.
> > */
> > copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
> > - hdr =3D &tmp_hdr;
> > } else {
> > - hdr =3D (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> > + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> > + (void *)(uintptr_t)buf_vec[0].buf_addr,
> > + sizeof(struct virtio_net_hdr));
> > }
> > + hdr =3D &tmp_hdr;
>=20
> Since this if block is just an optimization of the case where vnet header
> is contiguous why not just always use copy_vnet_hdr_from_desc? and inline=
it?
I also considered using the copy_vnet_hdr_from_desc function directly.
However, in most cases, the vnet header is continuous, and reusing
copy_vnet_hdr_from_desc results in additional operations.
Thanks,
Yunjian