netdev - Re: NAPI on USB network drivers

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Message-ID: <65d97336-d3c8-0fe7-659a-88ddecd1b13e@hartkopp.net>
Date:   Wed, 25 Jan 2017 14:33:51 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Hayes Wang <hayeswang@...ltek.com>,
        Oliver Neukum <oneukum@...e.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: NAPI on USB network drivers

On 01/25/2017 10:39 AM, Hayes Wang wrote:
> Oliver Neukum [mailto:oneukum@...e.com]
>> Sent: Wednesday, January 25, 2017 5:35 PM
> [...]
>> looking at r8152 I noticed that it uses NAPI. I never considered
>> this for the generic USB networking code as you cannot disable
>> interrupts for USB. Is it still worth it? What are the benefits?
>
> You could use napi_gro_receive() and it influences the performance.

Another positive effect with NAPI is that you won't face out-of-order 
ethernet frames as you get with non-NAPI drivers, e.g. ax88179_178a

http://marc.info/?l=linux-can&m=148049063812807&w=2

We have the issue with CAN drivers where all USB drivers and >90% of the 
I/O mapped drivers do not use NAPI.

I wonder whether it makes sense to add NAPI to a driver which only has 
ONE RX buffer ... but when searching for a solution for o-o-o frames I 
was always pointed to NAPI.

Regards,
Oliver