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

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Message-ID: <20171219095548.61d70d10@xeon-e3>
Date:   Tue, 19 Dec 2017 09:55:48 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, 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 Tue, 19 Dec 2017 09:41:39 -0800
"Samudrala, Sridhar" <sridhar.samudrala@...el.com> wrote:

> 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).
> 
> 
> 

could be 10ms, just enough to let udev do its renaming