netdev - Re: Question about __alloc

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Date:	Sun, 5 Dec 2010 18:56:24 +0800
From:	Junchang Wang <junchangwang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Question about __alloc_skb() speedup

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
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