netdev - Re: 2.6.24-rc2: Network commit causes SLUB performance regression with tbench

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Date:	Tue, 13 Nov 2007 22:37:26 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	nickpiggin@...oo.com.au
Cc:	clameter@....com, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au, linux-kernel@...r.kernel.org
Subject: Re: 2.6.24-rc2: Network commit causes SLUB performance regression
 with tbench

From: Nick Piggin <nickpiggin@...oo.com.au>
Date: Wed, 14 Nov 2007 05:14:27 +1100

> On Wednesday 14 November 2007 17:12, David Miller wrote:
> > Is your test system using HIGHMEM?
> >
> > That's one thing the page vector in the sk_buff can do a lot,
> > kmaps.
> 
> No, it's an x86-64, so no highmem.

Ok.

> What's also interesting is that SLAB apparently doesn't have this
> condition. The first thing that sprung to mind is that SLAB caches
> order > 0 allocations, while SLUB does not. However if anything,
> that should actually favour the SLUB numbers if network is avoiding
> order > 0 allocations.
> 
> I'm doing some oprofile runs now to see if I can get any more info.

Here are some other things you can play around with:

1) Monitor the values of skb->len and skb->data_len for packets
   going over loopback.

2) Try removing NETIF_F_SG in drivers/net/loopback.c's dev->feastures
   setting.
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