netdev - Re: [PATCH net-next] ibmvnic: Enable TSO support

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Date:   Thu, 25 May 2017 14:49:35 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     tlfalcon@...ux.vnet.ibm.com
Cc:     netdev@...r.kernel.org, nfont@...ux.vnet.ibm.com,
        jallen@...ux.vnet.ibm.com
Subject: Re: [PATCH net-next] ibmvnic: Enable TSO support

From: David Miller <davem@...emloft.net>
Date: Thu, 25 May 2017 14:46:26 -0400 (EDT)

> From: Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>
> Date: Wed, 24 May 2017 21:29:26 -0500
> 
>> The feature is also enabled by a module parameter.
>> This parameter is necessary because TSO can not easily be
>> enabled or disabled in firmware without reinitializing the driver.
> 
> Sorry, this is unacceptable.  When I say no module parameters,
> I really really mean it.
> 
> Users should not be burdoned with having to know a special knob for
> every driver in order to adjust what is a generic feature.
> 
> You'll have to find another way to accomodate this.

Also, TSO helps without SG only because you haven't implemented
support for xmit_more in this driver to decrease the number of
doorball updates and VM enters.

I bet if you added xmit_more support, TSO wouldn't give you much
if any performance boost if you have to linearize.