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Date: Sat, 23 Feb 2002 21:31:31 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: <mingo@elte.hu>
To: Larry McVoy <lm@bitmover.com>
Cc: Linus Torvalds <torvalds@transmeta.com>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Matthew Kirkwood <matthew@hairy.beasts.org>,
        Benjamin LaHaise <bcrl@redhat.com>, David Axmark <david@mysql.com>,
        William Lee Irwin III <wli@holomorphy.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Lightweight userspace semaphores...
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On Sat, 23 Feb 2002, Larry McVoy wrote:

> Exactly.  SMP gives you coherent memory and test-and-set or some other
> atomic operation.  Why not use it?

the userspace library side does it. The kernel patch is the slowpath, the
fast path (no contention) happens in user-space, using SMP-atomic
instructions. It's all very nice and lightweight.

also as far as i can see, this implementation enables semaphores to live
anywhere within the VM, the /dev/usem is just a hack to communicate this
VM address to the kernel-space code. So i think the patch's concepts are
really nice, except the interface cleanliness issue which shouldnt be too
hard to fix - adding new syscalls is pleasant work anyway :-)

	Ingo

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