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

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Message-Id: <20140227.130544.1892840202381139797.davem@davemloft.net>
Date:	Thu, 27 Feb 2014 13:05:44 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	swise@...ngridcomputing.com
Cc:	hariprasad@...lsio.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.

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.
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