From: "Jan Beulich" <JBeulich@suse.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: <mingo@elte.hu>,
"eric.dumazet@gmail.com" <eric.dumazet@gmail.com>,
<tglx@linutronix.de>, <luca@luca-barbieri.com>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] ix86: atomic64 assembly improvements
Date: Thu, 19 Jan 2012 15:11:54 +0000 [thread overview]
Message-ID: <4F1840CA020000780006DB79@nat28.tlf.novell.com> (raw)
In-Reply-To: <4F182FCB.2090300@zytor.com>
>>> On 19.01.12 at 15:59, "H. Peter Anvin" <hpa@zytor.com> wrote:
> On 01/19/2012 06:50 AM, Jan Beulich wrote:
>>>
>>> It doesn't have anything to do with caches on or off.
>>
>> How does it not? If any part of the bus topology is only 32 bits wide,
>> a 64-bit read or write simply can't be executed atomically without
>> asserting LOCK#.
>>
>
> Furthermore, if you're going down that rathole then we can't even trust
> MOV (nor, for that matter, can you trust LOCK in a lot of
No - (general register) MOV is at most 32 bits wide.
> circumstances.) In short, you need to be extremely careful about what
> you do to uncached memory *at all* (and you need to know exactly what is
> behind this bus) but pessimizing these kinds of construct for that
> reason is wrong in the extreme.
Okay, despite not being fully convinced I'll undo the folding of set and
xchg then, and re-submit.
Jan
prev parent reply other threads:[~2012-01-19 15:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-18 14:24 Jan Beulich
2012-01-18 16:36 ` H. Peter Anvin
2012-01-18 16:50 ` Jan Beulich
2012-01-18 17:47 ` H. Peter Anvin
2012-01-19 9:18 ` Jan Beulich
2012-01-19 14:44 ` H. Peter Anvin
2012-01-19 14:50 ` Jan Beulich
2012-01-19 14:55 ` H. Peter Anvin
2012-01-19 14:59 ` H. Peter Anvin
2012-01-19 15:11 ` Jan Beulich [this message]
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