Re: the arm cache coherency cluster "v2"

Andrew Jones
2015-03-18T19:11:55Z

On Wed, Mar 18, 2015 at 03:08:20PM -0400, Andrew Jones wrote:
> In reply to this message I'll send two series' one for KVM and
> one for QEMU. The two series' are their respective component
> complements, and attempt to implement cache coherency for arm
> guests using emulated devices, where the emulator (qemu) uses
> cached memory for the device memory, but the guest uses
> uncached - as device memory is generally used. Right now I've
> just focused on VGA vram.
>
> This approach is the "MADV_UNCACHED" type that Paolo suggested.
> This type of approach could also be described as "make userspace's
> memory access type match the expected access type of the guest",
> and Mario has suggested using a memory driver, which could have
> the same result.
>
> The coming series' is inspired by both Paolo's and Mario's
> suggestions, but it uses a kvm memslot flag, rather than an
> madvise flag, and thus for the memory driver, it's just KVM.
>
> See the thread
>
> https://lists.gnu.org/archive/html/qemu-devel/2015-03/msg01254.html
>
> for some more background.
>
> Thanks in advance for comments.
>
> drew

I forgot to mention that I've done some light testing with this.
It seems to work, and without (to eye) noticeable performance
degradation.

Thanks,
drew