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Date: Thu, 4 Sep 2014 17:50:44 +0100
From: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Jakub Jelinek <jakub@redhat.com>, Mikael Pettersson <mikpelinux@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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        linux-arch@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
        linux-ia64@vger.kernel.org
Subject: Re: bit fields && data tearing
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> Besides updating the documentation, it may make sense to do something
> arch-specific. Just bumping out storage on arches that don't need it
> seems wasteful, as does generating bus locks on arches that don't need it.
> Unfortunately, the code churn looks unavoidable.

The arch specific is pretty much set_bit and friends. Bus locks on a
locally owned cache line should not be very expensive on anything vaguely
modern, while uniprocessor boxes usually only have to generate set_bit
as a single instruction so it is interrupt safe.

Alan