linux-kernel - Re: Scalability requirements for sysv ipc (+namespaces broken with SEM

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Date:	Sun, 30 Mar 2008 19:18:08 +0200
From:	Mike Galbraith <efault@....de>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	paulmck@...ux.vnet.ibm.com, Nadia Derbey <Nadia.Derbey@...l.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Pavel Emelianov <xemul@...nvz.org>
Subject: Re: Scalability requirements for sysv ipc (+namespaces broken with
	SEM_UNDO)


On Sun, 2008-03-30 at 16:12 +0200, Manfred Spraul wrote:
> Mike Galbraith wrote:
> > On Sat, 2008-03-22 at 20:08 +0100, Manfred Spraul wrote:
> >
> >   
> >> just the normal performance of 2.6.25-rc3 is abyssimal, 55 to 60% slower 
> >> than 2.6.18.8:
> >>     
> >
> > After manually reverting 3e148c79938aa39035669c1cfa3ff60722134535,
> > 2.6.25.git scaled linearly
> We can't just revert that patch: with IDR, a global lock is mandatory :-(
> We must either revert the whole idea of using IDR or live with the 
> reduced scalability.

Yeah, I looked at the problem, but didn't know what the heck to do about
it, so just grabbed my axe to verify/quantify.

> Actually, there are further bugs: the undo structures are not 
> namespace-aware, thus semop with SEM_UNDO, unshare, create new array 
> with same id, but more semaphores, another semop with SEM_UNDO will 
> corrupt kernel memory :-(
> I'll try to clean up the bugs first, then I'll look at the scalability 
> again.

Great!

	-Mike


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