linux-kernel - Re: atomic RAM ?

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Message-ID: <4BBF2C5E.4060801@lumino.de>
Date:	Fri, 09 Apr 2010 15:32:14 +0200
From:	Michael Schnell <mschnell@...ino.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	nios2-dev <nios2-dev@...c.et.ntust.edu.tw>
Subject: Re: atomic RAM ?

On 04/09/2010 03:15 PM, Alan Cox wrote:
> Lamport's Bakery
Hmm. The code implements the lock as a busy spinning wait. This of
course is not possible in real world, as the thread that has the lock
will not get any CPU time (e.g. in a non-SMP system).

I understand that the main purpose of the FUTEX Kernel call(s) is doing
a not-busy wait and having the "unlock" code wake the (next) waiting thread.

I did implement something like this in my testing program: enhanced by a
sleep to allow for the thread that has the lock to proceed it's work,
but this of course is not fast at all, as a short sleep() produces too
much CPU load and a long sleep produces too much latency.

So maybe this algorithm can be used instead of the hardware stuff I
suggested but it would need a FUTEX-like Kernel part, too.

-Michael
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