netdev - Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe)

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Message-ID: <49FB27DE.6090002@cosmosbay.com>
Date:	Fri, 01 May 2009 18:48:30 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Miller <davem@...emloft.net>
CC:	andrew@...dna.net, jelaas@...il.com, netdev@...r.kernel.org
Subject: Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe)

David Miller a écrit :
> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Fri, 01 May 2009 08:14:03 +0200
> 
>> [PATCH] net: skb_tx_hash() improvements
>>
>> When skb_rx_queue_recorded() is true, we dont want to use jash distribution
>> as the device driver exactly told us which queue was selected at RX time.
>> jhash makes a statistical shuffle, but this wont work with 8 static inputs.
>>
>> Later improvements would be to compute reciprocal value of real_num_tx_queues
>> to avoid a divide here. But this computation should be done once,
>> when real_num_tx_queues is set. This needs a separate patch, and a new
>> field in struct net_device.
>>
>> Reported-by: Andrew Dickinson <andrew@...dna.net>
>> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> 
> Applied, except that I changed the commit message header line to more
> reflect that this is in fact a bug fix.
> 
> BTW, you don't need the reciprocol when num-tx-queues <= num-rx-queues
> (you can just use the RX queue recording as the hash, straight) and
> that's the kind of check what I intended to add to net-2.6 had you not
> beaten me to this patch.
> 
> Also, thanks for giving me absolutely no credit for this whole thing
> in your commit message.  I know I do that to you all the time :-/ How
> can you forget so quickly that I'm the one that even suggested the
> exact code change for Andrew to test in the first place?

Hoho, your Honor, I am totaly guilty and sorry, sometime I think I am
David Miller, silly me ! :)

I am not fighting for credit or whatever, certainly not with you.


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