From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Yang, Zhiyong" <zhiyong.yang@intel.com>
Subject: Re: [RFC PATCH] net/virtio: Align Virtio-net header on
 cache line in receive path
Date: Wed, 22 Feb 2017 02:49:05 +0000
Message-ID: <E182254E98A5DA4EB1E657AC7CB9BD2A3EB7257A@BGSMSX101.gar.corp.intel.com>
References: <20170221173243.20779-1-maxime.coquelin@redhat.com>
 <20170222013734.GJ18844@yliu-dev.sh.intel.com>
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Cc: "Liang, Cunming" <cunming.liang@intel.com>, "Tan, Jianfeng"
 <jianfeng.tan@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>, Maxime Coquelin
 <maxime.coquelin@redhat.com>
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> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Yuanhan Liu
> Sent: Wednesday, February 22, 2017 9:38 AM
> To: Maxime Coquelin <maxime.coquelin@redhat.com>
> Cc: Liang, Cunming <cunming.liang@intel.com>; Tan, Jianfeng
> <jianfeng.tan@intel.com>; dev@dpdk.org
> Subject: Re: [dpdk-dev] [RFC PATCH] net/virtio: Align Virtio-net header o=
n
> cache line in receive path
>=20
> On Tue, Feb 21, 2017 at 06:32:43PM +0100, Maxime Coquelin wrote:
> > This patch aligns the Virtio-net header on a cache-line boundary to
> > optimize cache utilization, as it puts the Virtio-net header (which is
> > always accessed) on the same cache line as the packet header.
> >
> > For example with an application that forwards packets at L2 level, a
> > single cache-line will be accessed with this patch, instead of two
> > before.
>=20
> I'm assuming you were testing pkt size <=3D (64 - hdr_size)?
>=20
> > In case of multi-buffers packets, next segments will be aligned on a
> > cache-line boundary, instead of cache-line boundary minus size of vnet
> > header before.
>=20
> The another thing is, this patch always makes the pkt data cache unaligne=
d
> for the first packet, which makes Zhihong's optimization on memcpy (for b=
ig
> packet) useless.

Why not could  we keep pkt data starting always on  the cache-line boundary=
?
In case of multi-buffer, the first remains unchanged, next segments can do =
as
Maxime said that.

Thanks
Zhiyong=20