linux-kernel - Re: Major regression on hackbench with SLUB (more numbers)

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Message-ID: <Pine.LNX.4.64.0712131416280.25120@schroedinger.engr.sgi.com>
Date:	Thu, 13 Dec 2007 14:22:18 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: Major regression on hackbench with SLUB (more numbers)

On Tue, 11 Dec 2007, Ingo Molnar wrote:

>     hackbench-10:      1.12             2.99   (166%)
>     hackbench-20:      2.04             6.67   (226%)
>     hackbench-50:      5.03            17.50   (247%)
> 
> and hackbench overhead stands out, by a huge margin. Other stuff is 
> within measurement noise. Neither SLUB nor SLAB debugging was turned on, 
> all other debugging options were off too.

I just came back from vacation. The non linear growth of regression
indicates lock contention somewhere. Must be something special that was 
triggered by hackbench.

We have had a regression like that in 2.6.24 before due to order 1 allocs 
in the network layer. The .24 modifications for SLUB introduced page 
allocator pass through for allocations > PAGESIZE/2. Order 1 allocs could 
serialize on zone locks.
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