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

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Message-Id: <20071113.175804.151698768.davem@davemloft.net>
Date:	Tue, 13 Nov 2007 17:58:04 -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: Tue, 13 Nov 2007 22:41:58 +1100

> On Tuesday 13 November 2007 06:44, Christoph Lameter wrote:
> > On Sat, 10 Nov 2007, Nick Piggin wrote:
> > > BTW. your size-2048 kmalloc cache is order-1 in the default setup,
> > > wheras kmalloc(1024) or kmalloc(4096) will be order-0 allocations. And
> > > SLAB also uses order-0 for size-2048. It would be nice if SLUB did the
> > > same...
> >
> > You can try to see the effect that order 0 would have by booting with
> >
> > slub_max_order=0
> 
> Yeah, that didn't help much, but in general I think it would give
> more consistent and reliable behaviour from slub.

Just a note that I'm not ignoring this issue, I just don't have time
to get to it yet.

I suspect the issue is about having a huge skb->data linear area for
TCP sends over loopback.  We're likely getting a much smaller
skb->data linear data area after the patch in question, the rest using
the sk_buff scatterlist pages which are a little bit more expensive to
process.

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