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

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Message-ID: <1393975366.16256.23.camel@deadeye.wl.decadent.org.uk>
Date:	Tue, 04 Mar 2014 23:22:46 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	swise@...ngridcomputing.com, 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.

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.

-- 
Ben Hutchings
I'm always amazed by the number of people who take up solipsism because
they heard someone else explain it. - E*Borg on alt.fan.pratchett

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