linux-kernel - Re: [PATCH 01 of 12] Core of mmu notifiers

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Message-ID: <20080429155030.GB28944@sgi.com>
Date:	Tue, 29 Apr 2008 10:50:30 -0500
From:	Robin Holt <holt@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Christoph Lameter <clameter@....com>, Robin Holt <holt@....com>,
	Jack Steiner <steiner@....com>, Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel@...ts.sourceforge.net,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>,
	linux-mm@...ck.org, general@...ts.openfabrics.org,
	Hugh Dickins <hugh@...itas.com>, akpm@...ux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 01 of 12] Core of mmu notifiers

> I however doubt this will bring us back to the same performance of the
> current spinlock version, as the real overhead should come out of
> overscheduling in down_write ai anon_vma_link. Here an initially
> spinning lock would help but that's gray area, it greatly depends on
> timings, and on very large systems where a cacheline wait with many
> cpus forking at the same time takes more than scheduling a semaphore
> may not slowdown performance that much. So I think the only way is a
> configuration option to switch the locking at compile time, then XPMEM
> will depend on that option to be on, I don't see a big deal and this
> guarantees embedded isn't screwed up by totally unnecessary locks on UP.

You have said this continually about a CONFIG option.  I am unsure how
that could be achieved.  Could you provide a patch?

Thanks,
Robin
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