From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Matan Azrad <matan@mellanox.com>, Noa Ezra <noae@mellanox.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 2/2] net/vhost: support mrg-rxbuf disabling
Date: Thu, 20 Jun 2019 09:19:23 +0200 [thread overview]
Message-ID: <59bce0c1-6f04-b743-c5fc-508b30e42075@redhat.com> (raw)
In-Reply-To: <AM0PR0502MB4019F26B82FF13C8930E6682D2E40@AM0PR0502MB4019.eurprd05.prod.outlook.com>
On 6/20/19 8:52 AM, Matan Azrad wrote:
> Hi all
>
>> -----Original Message-----
>> From: Noa Ezra
>> Sent: Thursday, June 20, 2019 8:58 AM
>> To: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Cc: Matan Azrad <matan@mellanox.com>; dev@dpdk.org
>> Subject: RE: [PATCH 2/2] net/vhost: support mrg-rxbuf disabling
>>
>> Hi Maxime,
>> Thanks for your comment, please see below.
>>
>>> -----Original Message-----
>>> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
>>> Sent: Wednesday, June 19, 2019 12:10 PM
>>> To: Noa Ezra <noae@mellanox.com>
>>> Cc: Matan Azrad <matan@mellanox.com>; dev@dpdk.org
>>> Subject: Re: [PATCH 2/2] net/vhost: support mrg-rxbuf disabling
>>>
>>> Hi Noa,
>>>
>>> On 6/19/19 8:13 AM, Noa Ezra wrote:
>>>> Rx mergeable buffers is a virtio feature that allows chaining of
>>>> multiple virtio descriptors to handle large packet size.
>>>> This behavior is supported and enabled by default, however in case
>>>> the user knows that rx mergeable buffers are not needed, he can
>>>> disable the feature.
>>>> The user should also set mrg_rxbuf=off in virtual machine's xml.
>>>
>>> I'm not sure to understand why it is needed, as the vhost-user library
>>> supports the feature, it's better to let it being advertised.
>>>
>>> As you say, it is up to the user to disable it in the VM's XML.
>>> Done this way, the feature won't be negotiated.
>>>
>> I agree with you, I'll remove this patch from the series.
>
> Are you sure that no performance impact exists for redundant merg-rx-buf configuration here?
I'm not sure to understand what you mean, could you please elaborate?
> What if the second side want it and the current side no?
The feature won't be negotiated, assuming it has been disabled in QEMU
cmdline (or via libvirt).
> It may be that the vhost PMD user may want to disable it to save performance from some reasons, no?
>
Then this user should disable it at QEMU level.
Regards,
Maxime
next prev parent reply other threads:[~2019-06-20 7:19 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-19 6:13 [dpdk-dev] [PATCH 0/2] support tso and " Noa Ezra
2019-06-19 6:13 ` [dpdk-dev] [PATCH 1/2] net/vhost: support TSO disabling Noa Ezra
2019-06-19 9:53 ` Maxime Coquelin
2019-06-20 2:26 ` Tiwei Bie
2019-06-20 6:08 ` Matan Azrad
2019-06-20 7:25 ` Maxime Coquelin
2019-08-30 8:44 ` Maxime Coquelin
2019-09-30 9:02 ` Maxime Coquelin
2019-06-19 6:13 ` [dpdk-dev] [PATCH 2/2] net/vhost: support mrg-rxbuf disabling Noa Ezra
2019-06-19 9:10 ` Maxime Coquelin
2019-06-20 5:57 ` Noa Ezra
2019-06-20 6:52 ` Matan Azrad
2019-06-20 7:19 ` Maxime Coquelin [this message]
2019-06-20 7:55 ` Matan Azrad
2019-06-26 7:50 ` Matan Azrad
2019-06-26 10:27 ` Maxime Coquelin
2019-06-26 11:18 ` Matan Azrad
2019-06-26 12:05 ` Maxime Coquelin
2019-06-26 13:24 ` Matan Azrad
2019-06-26 14:17 ` Maxime Coquelin
2019-06-27 5:04 ` Matan Azrad
2019-08-30 8:48 ` Maxime Coquelin
2019-06-20 7:27 ` Maxime Coquelin
2019-09-30 9:04 ` Maxime Coquelin
2019-06-19 14:20 ` [dpdk-dev] [PATCH 0/2] support tso and " Aaron Conole
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