netdev - Re: Question about __alloc

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Date:	Sun, 05 Dec 2010 17:49:16 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Junchang Wang <junchangwang@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Question about __alloc_skb() speedup

Le dimanche 05 décembre 2010 à 18:56 +0800, Junchang Wang a écrit :
> On Sat, Dec 04, 2010 at 03:47:38PM +0100, Eric Dumazet wrote:
> >
> >Yes I believe so, pktgen being very specific, but I have few questions :
> >
> >Is it with SLUB or SLAB ?
> I had read your discussion about "net: allocate skbs on local node" in
> the list, so SLUB was used.


> 
> BTW, what I observed is that network subsystem scales well on NUMA
> systems equipped with a single processor(up to six cores), but the
> performance didn't scale very well if there are two processors. 
> 
> I have noticed there are a number of discussions in the list. Are 
> there any suggestions? I'm very pleasant to do test.
> 
> >
> >How many buffers in TX ring on you nic (ethtool -g eth0) ?
> >
> Pre-set maximums:
> RX:             4096
> RX Mini:        0
> RX Jumbo:       0
> TX:             4096
> Current hardware settings:
> RX:             512
> RX Mini:        0
> RX Jumbo:       0
> TX:             512
> 
> >What is the datalen value here ? (you prefetch, then advance skb->data)
> >
> 16. But the following skb_push will drawback 14 bytes.
> 
> >32 or 64bit kernel ?
> >
> This is a CentOS 5.5 - 64bit distribution with the latest net-next.
> 
> >How many pps do you get before and after patch ?
> >
> A Intel SR1625 server with two E5530 quad-core processors and a single
> ixgbe-based NIC.
> Without prefetch: 8.63 Mpps
> With prefetch: 9.03 Mpps
> Improvement: 4.6%
> 
> 

Thanks Junchang, please submit your pktgen patch with the two added
prefetchw(), I'll Ack it :)



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