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Re: [Qemu-devel] [RFC v3 PATCH 14/14] target-i386: Generate fences for x

From: Pranith Kumar
Subject: Re: [Qemu-devel] [RFC v3 PATCH 14/14] target-i386: Generate fences for x86
Date: Tue, 21 Jun 2016 14:03:43 -0400

On Tue, Jun 21, 2016 at 1:54 PM, Peter Maydell <address@hidden> wrote:
> On 21 June 2016 at 18:28, Pranith Kumar <address@hidden> wrote:
>> Reg. the second point, I did consider this situation of running x86 on
>> ARM where such barriers are necessary for correctness. But, I am
>> really apprehensive of the cost it will impose. I am not sure if there
>> are any alternative solutions to avoid generating barriers for each
>> memory operation, but it would be great if we could reduce them.
> I vaguely recall an idea that you could avoid needing
> explicit barriers by turning all the guest load/stores into
> host load-acquire/store-release, but I have no idea whether
> that's (a) actually true (b) any better than piles of
> explicit barriers.

Yes, this is true for ARMv8(not sure about ia64). The
load-acquire/store-release operations are sequentially consistent to
each other. But this does not work for ARMv7 and as you said... I
think the cost here too is really prohibitive.


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