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

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Message-ID: <47EFB008.5080706@davidnewall.com>
Date:	Mon, 31 Mar 2008 01:51:44 +1030
From:	David Newall <davidn@...idnewall.com>
To:	Manfred Spraul <manfred@...orfullife.com>
CC:	Mike Galbraith <efault@....de>,
	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)

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.
>
> 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 :-(

You should revert it all.  The scalability problem isn't good, but from
what you're saying, the idea isn't ready yet.  Revert it all, fix the
problems at your leisure, and submit new patches then.
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