netdev - RE: [net-next 03/16] i40evf: Support RSS option in ethtool

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Date:	Fri, 28 Mar 2014 17:05:34 +0000
From:	"Williams, Mitch A" <mitch.a.williams@...el.com>
To:	Ben Hutchings <ben@...adent.org.uk>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>,
	"Sullivan, Catherine" <catherine.sullivan@...el.com>
Subject: RE: [net-next 03/16] i40evf: Support RSS option in ethtool



> -----Original Message-----
> From: Ben Hutchings [mailto:ben@...adent.org.uk]
> Sent: Thursday, March 27, 2014 5:14 PM
> To: Williams, Mitch A
> Cc: Kirsher, Jeffrey T; davem@...emloft.net; netdev@...r.kernel.org;
> gospo@...hat.com; sassmann@...hat.com; Sullivan, Catherine
> Subject: Re: [net-next 03/16] i40evf: Support RSS option in ethtool
> 
> On Wed, 2014-03-26 at 19:21 +0000, Williams, Mitch A wrote:
> >
> > > -----Original Message-----
> > > From: Ben Hutchings [mailto:ben@...adent.org.uk]
> > > Sent: Monday, March 17, 2014 11:54 AM
> > > To: Kirsher, Jeffrey T
> > > Cc: davem@...emloft.net; Williams, Mitch A; netdev@...r.kernel.org;
> > > gospo@...hat.com; sassmann@...hat.com; Sullivan, Catherine
> > > Subject: Re: [net-next 03/16] i40evf: Support RSS option in ethtool
> > >
> > > On Mon, 2014-03-17 at 05:45 -0700, Jeff Kirsher wrote:
> > > > From: Mitch Williams <mitch.a.williams@...el.com>
> > > >
> > > > Add support for viewing and modifying RSS hash options and RSS hash
> > > > look-up table programming through ethtool. Because the lookup table is
> > > > so small for the VFs (only 16 registers), we don't bother to maintain
> a
> > > > shadow table in memory, we just read and write the registers directly.
> > > [...]
> > > > +static int i40evf_get_rss_hash_opts(struct i40evf_adapter *adapter,
> > > > +				    struct ethtool_rxnfc *cmd)
> > > > +{
> > > > +	cmd->data = 0;
> > > > +
> > > > +	/* Report default options for RSS on i40e */
> > >
> > > But you're allowing them to be changed from the defaults, so this is
> > > wrong.
> >
> > Ben, I've got a question on this. Should the ETHTOOL_GRXFH option
> > report what the driver and device are capable of, or should it report
> > the current configuration?
> 
> It should report the current configuration.
> 
> > If this option is supposed to report device capabilities, how can we
> > find out the current configuration? And if it's supposed to report the
> > current configuration, then how do we find out the device
> > capabilities?
> 
> You can't find out the device capabilities except by trial and error (or
> driver-specific documentation).  Even if ETHTOOL_GRXFH did tell you
> which fields *could* be included in the hash, the structure doesn't have
> space to tell you which subsets are supported.
> 
> > I've been wading through the kernel source, and I see both. So I'm
> > confused.
> [...]
> 
> The first implementation was in niu, and in the absence of accompanying
> documentation that is what I took to define the interface and what I
> attempted to document in <linux/ethtool.h>.  If you think the current
> kernel-doc comment on struct ethtool_rxnfc is not clear enough, please
> do send a patch to improve the wording.
> 

Thanks, Ben. I'll make sure that the i40evf driver does the right thing.

-Mitch

> Ben.
> 
> --
> Ben Hutchings
> 73.46% of all statistics are made up.