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

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Message-ID: <47EF9FC2.3050901@colorfullife.com>
Date:	Sun, 30 Mar 2008 16:12:18 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Mike Galbraith <efault@....de>
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)

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 :-(
I'll try to clean up the bugs first, then I'll look at the scalability 
again.

--
    Manfred
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