netdev - Re: TCP transmit performance regression

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Message-ID: <CACVXFVPksMd8CGZWEGBXBXB5NZCg3QOZreOLavkV-Z2pjE-M_A@mail.gmail.com>
Date:	Thu, 5 Jul 2012 22:01:13 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: TCP transmit performance regression

On Thu, Jul 5, 2012 at 6:41 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2012-07-05 at 18:32 +0800, Ming Lei wrote:
>
>> After testing on beagle-xm, the patch is good and network is OK, but
>> iperf performance is still no improvement, see below:
>>
>> [root@...t]#iperf -c 192.168.0.103 -w 131072 -t 10
>> ------------------------------------------------------------
>> Client connecting to 192.168.0.103, TCP port 5001
>> TCP window size:   256 KByte (WARNING: requested   128 KByte)
>> ------------------------------------------------------------
>> [  3] local 192.168.0.119 port 46776 connected with 192.168.0.103 port 5001
>> [ ID] Interval       Transfer     Bandwidth
>> [  3]  0.0-10.0 sec  41.4 MBytes  34.7 Mbits/sec
>>
>
> I fear there are copies in the tx path as well, in smsc95xx_tx_fixup()

Basically, copy path will be bypassed since hard_header_len
has included the 'overhead' already.

> (SLAB debug is going to cost a lot with big bufers)

At default SMSC95xx turbo mode is true, rx buffer will be very big
(17.5K). Or the large rx buffer size puts limit on concurrent URBs/SKBs
count.  Both two may cause the problem.

Thanks,
-- 
Ming Lei
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