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

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Date:   Tue, 19 Dec 2017 10:13:45 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.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 20:07:01 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Tue, Dec 19, 2017 at 09:55:48AM -0800, Stephen Hemminger wrote:
> > 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  
> 
> Isn't there a way not to depend on udev completing its thing within a given timeframe?

Not that I know. the path is quite indirect.