netdev - Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when available

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Message-ID: <87efnplljl.fsf@vitty.brq.redhat.com>
Date:   Wed, 20 Dec 2017 11:51:26 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     sridhar.samudrala@...el.com, mst@...hat.com,
        netdev@...r.kernel.org, alexander.duyck@...il.com,
        virtualization@...ts.linux-foundation.org,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when available

David Miller <davem@...emloft.net> writes:

> From: "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
> Date: Tue, 19 Dec 2017 09:41:39 -0800
>
>> This is based on netvsc implementation and here is the commit that
>> added this delay.  Not sure if this needs to be 100ms.
>> 
>> commit 6123c66854c174e4982f98195100c1d990f9e5e6
>> Author: stephen hemminger <stephen@...workplumber.org>
>> Date:   Wed Aug 9 17:46:03 2017 -0700
>> 
>>     netvsc: delay setup of VF device
>> 
>>     When VF device is discovered, delay bring it automatically up in
>>     order to allow userspace to some simple changes (like renaming).
>
> This is kind of bogus, I should have called this out when the patch
> was posted.
>
> Any delay is wrong, there needs to be tight synchronization if a
> userspace operation must occur before proceeding.  If something
> happens and userspace is delayed, this whole thing doesn't work.

Hyper-V's netvsc does exactly the same and when this was first discussed
I suggested to allow renaming of IFF_UP interfaces:
https://patchwork.kernel.org/patch/9890299/

but as far as I understand it was decided that it's too risky and not
worth it. Maybe we need to reconsider this, at least for slave
interfaces (as scripts are not supposed to operate on them).

-- 
  Vitaly