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Re: [Qemu-discuss] Getting qemu-system-i386 to use more than one core on

From: Peter Maydell
Subject: Re: [Qemu-discuss] Getting qemu-system-i386 to use more than one core on Cortex A7 host
Date: Mon, 4 Jan 2016 21:29:34 +0000

On 4 January 2016 at 13:24, Jakob Bohm <address@hidden> wrote:
> For your information, the x86 memory model only requires
> barriers in the following cases (this is somewhat
> implemented on modern machines with multiple actual x86
> CPU sockets, as opposed to multicore chips, it may also
> be observed when using any kind of DMA/bus-master
> hardware such as GPUs):

[list elided]

> This still leaves the majority of code not doing memory barriers.

This implies that x86 has no stricter restrictions on
reordering of plain loads and stores than ARM does. That
surprises me -- I thought x86's memory model imposed
stricter constraints on the implementation. (For instance
lists several cases like load-after-load that ARM might
reorder but x86 forbids reordering for.)

But I haven't looked into the details beyond mentally
tagging the situation as "here be dragons" for if/when
I ever need to review any code dealing with it.

-- PMM

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