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

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Date:   Tue, 19 Dec 2017 13:20:17 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sridhar.samudrala@...el.com
Cc:     mst@...hat.com, stephen@...workplumber.org, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        alexander.duyck@...il.com, jesse.brandeburg@...el.com
Subject: Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when
 available

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.