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

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Date:   Tue, 19 Dec 2017 09:41:39 -0800
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     stephen@...workplumber.org, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        alexander.duyck@...il.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Subject: Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when
 available


On 12/19/2017 7:47 AM, Michael S. Tsirkin wrote:
> I'll need to look at this more, in particular the feature
> bit is missing here. For now one question:
>
> On Mon, Dec 18, 2017 at 04:40:36PM -0800, Sridhar Samudrala wrote:
>> @@ -56,6 +58,8 @@ module_param(napi_tx, bool, 0644);
>>    */
>>   DECLARE_EWMA(pkt_len, 0, 64)
>>   
>> +#define VF_TAKEOVER_INT	(HZ / 10)
>> +
>>   #define VIRTNET_DRIVER_VERSION "1.0.0"
>>   
>>   static const unsigned long guest_offloads[] = {
> Why is this delay necessary? And why by 100ms?

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).