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Date: Thu, 04 Sep 2014 15:42:35 -0400
From: Peter Hurley <peter@hurleysoftware.com>
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To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Subject: Re: bit fields && data tearing
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Cc: Jakub Jelinek <jakub@redhat.com>, Mikael Pettersson <mikpelinux@gmail.com>,
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 Paul Mackerras <paulus@samba.org>, linux-arch@vger.kernel.org,
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On 09/04/2014 12:50 PM, One Thousand Gnomes wrote:
>> 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.

Or we could give up on the Alpha.

It's not just the non-atomic bytes; we could do away with the
read_barrier_depends() which hardly any code gets correctly anyway.

Regards,
Peter Hurley