netdev - Re: e1000 performance issue in 4 simultaneous links

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Message-ID: <47879DE4.8080603@cosmosbay.com>
Date:	Fri, 11 Jan 2008 17:48:36 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Breno Leitao <leitao@...ux.vnet.ibm.com>
Cc:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	rick.jones2@...com, netdev@...r.kernel.org
Subject: Re: e1000 performance issue in 4 simultaneous links

Breno Leitao a écrit :
> On Thu, 2008-01-10 at 12:52 -0800, Brandeburg, Jesse wrote:
>   
>> Breno Leitao wrote:
>>     
>>> When I run netperf in just one interface, I get 940.95 * 10^6 bits/sec
>>> of transfer rate. If I run 4 netperf against 4 different interfaces, I
>>> get around 720 * 10^6 bits/sec.
>>>       
>> I hope this explanation makes sense, but what it comes down to is that
>> combining hardware round robin balancing with NAPI is a BAD IDEA.  In
>> general the behavior of hardware round robin balancing is bad and I'm
>> sure it is causing all sorts of other performance issues that you may
>> not even be aware of.
>>     
> I've made another test removing the ppc IRQ Round Robin scheme, bonded
> each interface (eth6, eth7, eth16 and eth17) to different CPUs (CPU1,
> CPU2, CPU3 and CPU4) and I also get around around 720 * 10^6 bits/s in
> average.
>
> Take a look at the interrupt table this time: 
>
> io-dolphins:~/leitao # cat /proc/interrupts  | grep eth[1]*[67]
> 277:         15    1362450         13         14         13         14         15         18   XICS      Level     eth6
> 278:         12         13    1348681         19         13         15         10         11   XICS      Level     eth7
> 323:         11         18         17    1348426         18         11         11         13   XICS      Level     eth16
> 324:         12         16         11         19    1402709         13         14         11   XICS      Level     eth17
>
>
> I also tried to bound all the 4 interface IRQ to a single CPU (CPU0)
> using the noirqdistrib boot paramenter, and the performance was a little
> worse.
>
> Rick, 
>   The 2 interface test that I showed in my first email, was run in two
> different NIC. Also, I am running netperf with the following command
> "netperf -H <hostname> -T 0,8" while netserver is running without any
> argument at all. Also, running vmstat in parallel shows that there is no
> bottleneck in the CPU. Take a look: 
>
> procs -----------memory---------- ---swap-- -----io---- -system-- -----cpu------
>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
>  2  0      0 6714732  16168 227440    0    0     8     2  203   21  0  1 98  0  0
>  0  0      0 6715120  16176 227440    0    0     0    28 16234  505  0 16 83  0  1
>  0  0      0 6715516  16176 227440    0    0     0     0 16251  518  0 16 83  0  1
>  1  0      0 6715252  16176 227440    0    0     0     1 16316  497  0 15 84  0  1
>  0  0      0 6716092  16176 227440    0    0     0     0 16300  520  0 16 83  0  1
>  0  0      0 6716320  16180 227440    0    0     0     1 16354  486  0 15 84  0  1
>  
>
>   
If your machine has 8 cpus, then your vmstat output shows a bottleneck :)

(100/8 = 12.5), so I guess one of your CPU is full





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