netdev - Re: net: more accurate skb truesize

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Date:	Tue, 10 Apr 2012 13:38:33 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev@...r.kernel.org,
	John Williams <john.williams@...alogix.com>,
	David Miller <davem@...emloft.net>
Subject: Re: net: more accurate skb truesize - regression on Microblaze

On 04/10/2012 01:32 PM, Eric Dumazet wrote:
> On Tue, 2012-04-10 at 10:37 +0200, Michal Simek wrote:
>> On 04/10/2012 10:32 AM, Eric Dumazet wrote:
>>> On Tue, 2012-04-10 at 10:27 +0200, Eric Dumazet wrote:
>>>
>>>> BTW, some NIC drivers are known to provide fat skb in their rx path, and
>>>> need to be fixed as well. (Some others just lie about skb->truesize to
>>>> avoid the tcp slowdown, see my previous iwlwifi patch)
>>>>
>>>>
>>>
>>> What is the driver you currently use on your platform ?
>>
>> Using Xilinx ll_temac(in mainline) and axi_emac.
>>
>
> ll_temac allocates XTE_MAX_JUMBO_FRAME_SIZE frames, even for MTU=1500 ?

yes.

>
> Trying to allocate smaller packets would definitely help your tcp
> receiver performance and overall reliability  (order-0 allocations
> instead of order-2)

There is long history for ll_temac and axi emac drivers. and if you compare
them they are very similar with similar bugs.
In our distribution we are using older ll_temac driver where this is fixed.
Performance is much higher if you allocate buffers for actual mtu.

Thanks,
Michal

P.S.: Our plan is to start to use mainline drivers and fixing them to get
the same performance as we have with old one. It is one my todo list.


-- 
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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