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

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Date:	Thu, 27 Feb 2014 11:11:49 -0600
From:	"Steve Wise" <swise@...ngridcomputing.com>
To:	"'David Miller'" <davem@...emloft.net>, <hariprasad@...lsio.com>
Cc:	<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.

> 
> > -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.

Steve.

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