From: Paolo Bonzini <pbonzini@redhat.com>
To: Mark Burton <mark.burton@greensocs.com>
Cc: mttcg@greensocs.com, "Peter Maydell" <peter.maydell@linaro.org>,
"Alexander Graf" <agraf@suse.de>,
"QEMU Developers" <qemu-devel@nongnu.org>,
"Guillaume Delbergue" <guillaume.delbergue@greensocs.com>,
"Alex Bennée" <alex.bennee@linaro.org>,
"KONRAD Frédéric" <fred.konrad@greensocs.com>
Subject: Re: [Qemu-devel] [RFC PATCH V3] Use atomic cmpxchg to atomically check the exclusive value in a STREX
Date: Fri, 19 Jun 2015 09:42:08 +0200 [thread overview]
Message-ID: <5583C7D0.6050908@redhat.com> (raw)
In-Reply-To: <18093935-2D4D-43F3-90AA-48832146FB7B@greensocs.com>
On 19/06/2015 09:40, Mark Burton wrote:
>> On 19/06/2015 09:29, Mark Burton wrote:
>>> Does anybody know if the current atomic_cmpxchg will support
>>> 64 bit on a (normal) 32 bit x86, or do we need to special
>>> case that with cmpxchg8b ? (I get the impression that it will
>>> automatically use cmpxchg8b, but not cmpxchg16b - but I’m by
>>> no means sure).
>>
>> Both cmpxchg8b and cmpxchg16b are used, respectively on 32-bit
>> and 64-bit x86.
>
> Thanks Paolo, so we are OK for x86, but we would need to disable
> multi-thread for other 32 bit hosts, and provide a correct
> implementation for non multi-thread…
But Alvise's implementation for example would work there. It is just
this optimization (that is also not architecturally correct on ARM) that
is problematic.
Paolo
> You dont happen to know of a
> convenient macro we can use to test for ’32 bit hosts that dont
> support 64bit cmpxchg ….’
next prev parent reply other threads:[~2015-06-19 7:42 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-18 15:44 [Qemu-devel] [RFC PATCH V3] Use atomic cmpxchg to atomically check the exclusive value in a STREX fred.konrad
2015-06-18 15:46 ` Paolo Bonzini
2015-06-18 15:56 ` Peter Maydell
2015-06-18 18:32 ` Mark Burton
2015-06-18 19:53 ` Peter Maydell
2015-06-19 7:29 ` Mark Burton
2015-06-19 7:31 ` Paolo Bonzini
2015-06-19 7:40 ` Mark Burton
2015-06-19 7:42 ` Paolo Bonzini [this message]
2015-06-19 7:43 ` Mark Burton
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