netdev - Re: net: more accurate skb truesize

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Date:	Tue, 10 Apr 2012 14:12:51 +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 01:50 PM, Eric Dumazet wrote:
> On Tue, 2012-04-10 at 13:38 +0200, Michal Simek wrote:
>> On 04/10/2012 01:32 PM, Eric Dumazet wrote:
>>>
>>> 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.
>
> Ah good, because this 9000+pad versus 1500+pad allocation is way more
> problematic than the (small) change on skb->truesize you bisected ;)

yeah I know. Currently for me is the most important thing to have stable
driver which is ancient one and start to work on mainline to add there all features
and do more testing before we will add it to customers.

I have found it because I have compared the same driver with different kernel
versions and there was performance regression. Comparing with old one will show
different results. :-)

I will keep you in the loop when I start to fix mainline driver.

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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