netdev - Re: [RFC] bnx2x: Insane RX rings

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Date:	Thu, 09 Sep 2010 14:30:01 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ole@....pl
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org, eilong@...adcom.com
Subject: Re: [RFC] bnx2x: Insane RX rings

From: Krzysztof Olędzki <ole@....pl>
Date: Thu, 09 Sep 2010 23:21:01 +0200

> On 2010-09-09 22:45, Eric Dumazet wrote:
>> Problem is : With 16 RX queues per device , thats 4078*16*2Kbytes per
>> ethernet port.
>>
>> Total :
>>
>> skbuff_head_cache 130747 131025 256 15 1 : tunables 120 60 8 :
>> slabdata 8735 8735 40
>> size-2048 130866 130888 2048 2 1 : tunables 24 12 8 : slabdata 65444
>> 65444 28
>>
>> Thats about 300 Mbytes of memory, just in case some network trafic
>> will occur.
>>
>> Lets do something about that ?
> 
> Yep, it is ~8MB per queue, not so much alone, but a lot together. For
> this reason I use something like bnx2.num_queues=2 on servers where I
> don't need much CPU power for network workload.

I think simply that the RX queue size should be scaled by the number
of queues we have.

If people want enormous RX ring sizes even when there are many queues,
they can use ethtool to get that.

Taking up 130MB of memory per-card, just for RX packet buffers, is
certainly over the top.
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