netdev - RE: [EXT] Re: [PATCH net-next 07/10] qed*: Add iWARP 100g support

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Message-ID: <BLUPR18MB0130AF99D6AB674A85E075D9A1340@BLUPR18MB0130.namprd18.prod.outlook.com>
Date:   Thu, 2 May 2019 12:10:39 +0000
From:   Michal Kalderon <mkalderon@...vell.com>
To:     Leon Romanovsky <leon@...nel.org>,
        David Miller <davem@...emloft.net>
CC:     Ariel Elior <aelior@...vell.com>, "jgg@...pe.ca" <jgg@...pe.ca>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH net-next 07/10] qed*: Add iWARP 100g support

> From: Leon Romanovsky <leon@...nel.org>
> Sent: Thursday, May 2, 2019 8:13 AM
> On Wed, May 01, 2019 at 08:35:22PM -0400, David Miller wrote:
> > From: Michal Kalderon <michal.kalderon@...vell.com>
> > Date: Wed, 1 May 2019 12:57:19 +0300
> >
> > > diff --git a/drivers/infiniband/hw/qedr/main.c
> > > b/drivers/infiniband/hw/qedr/main.c
> > > index d93c8a893a89..8bc6775abb79 100644
> > > --- a/drivers/infiniband/hw/qedr/main.c
> > > +++ b/drivers/infiniband/hw/qedr/main.c
> > > @@ -52,6 +52,10 @@ MODULE_DESCRIPTION("QLogic 40G/100G ROCE
> > > Driver");  MODULE_AUTHOR("QLogic Corporation");
> > > MODULE_LICENSE("Dual BSD/GPL");
> > >
> > > +static uint iwarp_cmt;
> > > +module_param(iwarp_cmt, uint, 0444);
> MODULE_PARM_DESC(iwarp_cmt, "
> > > +iWARP: Support CMT mode. 0 - Disabled, 1 - Enabled. Default:
> > > +Disabled");
> > > +
> >
> > Sorry no, this is totally beneath us.
> 
> It is not acceptable for RDMA too.

Dave and Leon, 

This is a bit of a special case related specifically to our hardware.
Enabling iWARP on this kind of configuration impacts L2 performance.
We don't want this to happen implicitly once the rdma driver is loaded since
that can happen automatically and could lead to unexpected behavior from user perspective.
Therefore we need a way of giving the user control to decide whether they want iWARP at the cost
of L2 performance degradation.
We also need this information as soon as the iWARP device registers, so using the rdma-tool would be too late.

If module parameter is not an option, could you please advise what would be ok ? 
ethtool private flags ? 
devlink ? 

thanks,
Michal

> 
> Also please don't use comments inside function calls, it complicates various
> checkers without real need.
> dev->ops->iwarp_set_engine_affin(dev->cdev, true /* reset */);
>                                                 ^^^^^^^^^^^^^^ Thanks