netdev - Re: Multicast packet loss

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Message-ID: <20090203115502.GB28117@hmsreliant.think-freely.org>
Date:	Tue, 3 Feb 2009 06:55:02 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Kenny Chang <kchang@...enacr.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Multicast packet loss

On Mon, Feb 02, 2009 at 11:48:25AM -0500, Kenny Chang wrote:
> Neil Horman wrote:
>> On Fri, Jan 30, 2009 at 11:41:23PM +0100, Eric Dumazet wrote:
>>   
>>> Kenny Chang a écrit :
>>>     
>>>> Ah, sorry, here's the test program attached.
>>>>
>>>> We've tried 2.6.28.1, but no, we haven't tried the 2.6.28.2 or the
>>>> 2.6.29.-rcX.
>>>>
>>>> Right now, we are trying to step through the kernel versions until we
>>>> see where the performance drops significantly.  We'll try 2.6.29-rc soon
>>>> and post the result.
>>>>       
>>> 2.6.29-rc contains UDP receive improvements (lockless)
>>>
>>> Problem is multicast handling was not yet updated, but could be :)
>>>
>>>
>>> I was asking you "cat /proc/interrupts" because I believe you might
>>> have a problem NIC interrupts being handled by one CPU only (when having problems)
>>>
>>>     
>> That would be expected (if irqbalance is running), and desireable, since
>> spreading high volume interrupts like NICS accross multiple cores (or more
>> specifically multiple L2 caches), is going increase your cache line miss rate
>> significantly and decrease rx throughput.
>>
>> Although you do have a point here, if the system isn't running irqbalance, and
>> the NICS irq affinity is spread accross multiple L2 caches, that would be a
>> point of improvement performance-wise.  
>>
>> Kenny, if you could provide the /proc/interrupts info along with /proc/cpuinfo
>> and your stats that I asked about earlier, that would be a big help.
>>
>> Regards
>> Neil
>>
>>   
> This is for a working setup.
>

Are these quad core systems?  Or dual core w/ hyperthreading?  I ask because in
your working setup you have 1/2 the number of cpus' and was not sure if you
removed an entire package of if you just disabled hyperthreading.


Neil

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