netdev - Re: Add NAPI support to ll

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Message-ID: <4DAD8B8E.1010008@monstr.eu>
Date:	Tue, 19 Apr 2011 15:18:06 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: Add NAPI support to ll_temac driver

Ben Hutchings wrote:
> On Tue, 2011-04-19 at 14:48 +0200, Michal Simek wrote:
>> Ben Hutchings wrote:
>>> On Tue, 2011-04-19 at 12:43 +0200, Eric Dumazet wrote:
>>> [...]
>>>> One possible way to get better performance is to change driver to
>>>> allocate skbs only right before calling netif_rx(), so that you dont
>>>> have to access cold sk_buff data twice (once when allocating skb and put
>>>> it in ring buffer, a second time when receiving frame)
>>>>
>>>> drivers/net/niu.c is a good example for this (NAPI + netdev_alloc_skb()
>>>> just in time + pull in skbhead only first cache line of packet)
>>> [...]
>>>
>>> If the hardware can do RX checksumming (it's not clear) then the driver
>>> should pass the paged buffers into GRO and that will take care of skb
>>> allocation as necessary.
>> Hardware supports RX and TX partial checksumming. I can enable it. The driver 
>> has also this option and from my tests there is of course some performance 
>> improvemetn.
>>
>> Just for sure - here are links on documentation.
>> http://www.xilinx.com/support/documentation/ip_documentation/xps_ll_temac.pdf
>> or
>> http://www.xilinx.com/support/documentation/ip_documentation/axi_ethernet/v2_01_a/ds759_axi_ethernet.pdf
> 
> I'm not going to read those.  Just providing brief advice.
> 
>> About SKB allocation. I fixed our non mainline driver to allocate skb based on 
>> current mtu size. Mainline driver allocate max mtu (9k). This has also impact on 
>> performance because Microblaze works with smaller SKBs.
>>
>> Can you please be more specific about passing the paged buffers into GRO?
>> Or point me to any documentation or code which can help me to understand what 
>> that means.
> 
> You would use napi_get_frags() to get a new or recycled skb, fill in
> skb->frags, then call napi_gro_frags() to pass it into GRO.  The benet,
> cxgb3 and sfc drivers do this.

ok. Will look.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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