netdev - Re: [PATCH net-next 10/31] cxgb4/iw_cxgb4: Doorbell Drop Avoidance Bug Fixes.

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Date:	Wed, 5 Mar 2014 11:04:14 +0530
From:	Hariprasad S <hariprasad@...lsio.com>
To:	Ben Hutchings <ben@...adent.org.uk>,
	David Miller <davem@...emloft.net>
CC:	<swise@...ngridcomputing.com>, <netdev@...r.kernel.org>,
	<linux-rdma@...r.kernel.org>, <roland@...estorage.com>,
	<kumaras@...lsio.com>, <dm@...lsio.com>, <leedom@...lsio.com>,
	<santosh@...lsio.com>, <nirranjan@...lsio.com>
Subject: Re: [PATCH net-next 10/31] cxgb4/iw_cxgb4: Doorbell Drop Avoidance
 Bug Fixes.

On Tue, Mar 04, 2014 at 23:22:46 +0000, Ben Hutchings wrote:
> On Thu, 2014-02-27 at 13:05 -0500, David Miller wrote:
> > From: "Steve Wise" <swise@...ngridcomputing.com>
> > Date: Thu, 27 Feb 2014 11:11:49 -0600
> > 
> > >> 
> > >> > -static int allow_db_fc_on_t5;
> > >> > -module_param(allow_db_fc_on_t5, int, 0644);
> > >> > -MODULE_PARM_DESC(allow_db_fc_on_t5,
> > >> > -           "Allow DB Flow Control on T5 (default = 0)");
> > >> > -
> > >> > -static int allow_db_coalescing_on_t5;
> > >> > -module_param(allow_db_coalescing_on_t5, int, 0644);
> > >> > -MODULE_PARM_DESC(allow_db_coalescing_on_t5,
> > >> > -           "Allow DB Coalescing on T5 (default = 0)");
> > >> 
> > >> Module parameters are a user facing interface.
> > >> 
> > >> You cannot just delete, or change the semantics of, the ones you feel
> > >> like doing so to.
> > > 
> > > I see your point on user facing interfaces.   These module params were
> > > added initially to allow tweaking the db drop recovery for T5 devices in
> > > the thought that we might need it.  It turns out T5 doesn't suffer from
> > > this issue.  These params default to 0 anyway, and I doubt anyone has
> > > changed them.  Disabling the hw db coalescing feature proved problematic
> > > and it turned out to even make the issue worse, so I removed it totally
> > > at the recommendation from the HW engineers, and put in place the new
> > > design which better rate controls things under heavy load.
> > 
> > You have to keep the old ones around.
> 
> Setting an unknown module parameter now results in a warning (since
> 3.11), so removing a parameter isn't so disruptive as it used to be.
> 
> Obviously this is removing a feature, but as the feature sounds like it
> was only marginally useful I think it's a perfectly valid change.
> 
> Ben.

Thanks Ben for letting us know that things have changed post 3.11 kernel.

Hi David,
Would you be OK if we remove the unused module_param now when we re-submit the series ?


Thanks,
-Hari.
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