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Re: Emulating CPUs with larger atomic accesses
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From: |
Florian Weimer |
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Subject: |
Re: Emulating CPUs with larger atomic accesses |
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Date: |
Tue, 24 May 2022 11:27:24 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
* Richard Henderson:
> On 5/13/22 03:00, Florian Weimer wrote:
>> What's QEMU's approach to emulating CPU instructions that atomatically
>> operate on values larger than what is supported by the host CPU?
>> I assume that for full system emulation, this is not a problem, but
>> qemu-user will not achieve atomic behavior on shared memory mappings.
>> How much of a problem is this in practice?
>
> Well, it doesn't work, no. In practice, x86_64 supports 128-bit
> atomic operations, and guest requires more than that. No one really
> cares anymore about 32-bit hosts with smaller atomic operations.
Which part doesn't work? Full-system emulation?
Do guests really require wider-than-128 atomics? That's quite
surprising?
Thanks,
Florian