netdev - Re: [virtio-dev] RE: [PATCH v5 2/2] virtio-net: use mtu size as buffer length for big packets

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Date:   Wed, 7 Sep 2022 15:57:33 -0700
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     Parav Pandit <parav@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Gavin Li <gavinl@...dia.com>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "jesse.brandeburg@...el.com" <jesse.brandeburg@...el.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "sridhar.samudrala@...el.com" <sridhar.samudrala@...el.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "loseweigh@...il.com" <loseweigh@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        Gavi Teitz <gavi@...dia.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [virtio-dev] RE: [PATCH v5 2/2] virtio-net: use mtu size as
 buffer length for big packets



On 9/7/2022 3:11 PM, Parav Pandit wrote:
>> From: Si-Wei Liu <si-wei.liu@...cle.com>
>> Sent: Wednesday, September 7, 2022 5:40 PM
>>
>>
>> On 9/7/2022 12:51 PM, Parav Pandit wrote:
>>>> And I'd like commit log to include results of perf testing
>>>> - with indirect feature on
>>> Which device do you suggest using for this test?
>>>
>> You may use software vhost-net backend with and without fix to compare.
>> Since this driver fix effectively lowers down the buffer size for the
>> indirect=on case as well,
> Do you have sample example for this?

ip link add link ens300f1 name macvtap1 address $mac type macvtap mode 
bridge
ifindex1=`cat /sys/class/net/macvtap1/ifindex`

qemu-system-x86_64 \
   ...
   -netdev type=tap,id=hnet1,vhost=on,fd=25,vhostfd=27 \
   -device 
virtio-net-pci,netdev=hnet1,id=vnet1,mac=$mac,host_mtu=9000,mrg_rxbuf=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off,indirect_desc=on 
\
   25<>/dev/tap${ifindex1} 27<>/dev/vhost-net

indirect_desc=on is not actually required as it's on by default if not 
specified.

-Siwei