On 02/22/2017 03:49 AM, Yang, Zhiyong wrote:
-----Original Message-----
From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Yuanhan Liu
Sent: Wednesday, February 22, 2017 9:38 AM
To: Maxime Coquelin <maxime.coque...@redhat.com>
Cc: Liang, Cunming <cunming.li...@intel.com>; Tan, Jianfeng
<jianfeng....@intel.com>; dev@dpdk.org
Subject: Re: [dpdk-dev] [RFC PATCH] net/virtio: Align Virtio-net header on
cache line in receive path
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.
I'm assuming you were testing pkt size <= (64 - hdr_size)?
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.
The another thing is, this patch always makes the pkt data cache unaligned
for the first packet, which makes Zhihong's optimization on memcpy (for big
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.
This is not possible to have both the first and next buffers aligned on
cache line boundary, as we don't know whether the deccriptor will be the
first one, or a subsequent one on Virtio side when we refill the vq.
Cheers,
Maxime
Thanks
Zhiyong
