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Message-ID: <48B81F60.3080409@gmail.com>
Date: Fri, 29 Aug 2008 12:10:08 -0400
From: Gregory Haskins <gregory.haskins@gmail.com>
User-Agent: Thunderbird 2.0.0.16 (X11/20080720)
MIME-Version: 1.0
To: Andi Kleen <andi@firstfloor.org>
CC: Gregory Haskins <ghaskins@novell.com>, mingo@elte.hu, rostedt@goodmis.org,
       tglx@linutronix.de, linux-kernel@vger.kernel.org,
       linux-rt-users@vger.kernel.org
Subject: Re: [PATCH] seqlock: serialize against writers
References: <20080829154237.1196.66825.stgit@dev.haskins.net> <87abevpzv7.fsf@basil.nowhere.org>
In-Reply-To: <87abevpzv7.fsf@basil.nowhere.org>
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Andi Kleen wrote:
> Gregory Haskins <ghaskins@novell.com> writes:
>
>  =20
>> *Patch submitted for inclusion in PREEMPT_RT 26-rt4.  Applies to 2.6.2=
6.3-rt3*
>>
>> Hi Ingo, Steven, Thomas,
>>   Please consider for -rt4.  This fixes a nasty deadlock on my systems=
 under
>>   heavy load.
>>    =20
>
> Does this even work under x86-64? x86-64 uses seqlocks in user space
> in its vsyscalls. And read_lock() definitely doesn't work there because=
=20
> it writes.
>
> You would need at least to disable vsyscall gettimeofday(), making
> it much much slower.
>
> Perhaps you tested on one of the systems where the vsyscalls need
> to fallback for other reasons? (e.g. one using pmtimer for timing).
>
> -Andi
>  =20

Im running it on a x86_64 box as we speak.  How can I tell if there is a
certain mode that is permitting this?

-Greg


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