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Re: [Qemu-devel] [PATCH v2 0/5] AArch64 TLB performance improvements


From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH v2 0/5] AArch64 TLB performance improvements
Date: Mon, 4 Aug 2014 11:32:42 +0100

On 4 August 2014 11:23, Alex Bennée <address@hidden> wrote:
> Peter Maydell writes:
>> So:
>>  * there's clearly a big perf win to be had here
>>  * this patchset gives us that for 4K pages on AArch64
>>  * but it doesn't help for 4K pages on AArch32 (really
>>     common)
>
> Well for the AArch32 profile if you ran under qemu-system-aarch64 you
> would be OK surely?

Yes, but that's pretty non-obvious, and also it doesn't
make much sense to the user to say "these 32 bit
CPUs should be run under qemu-system-aarch64 but
these other ones should be under qemu-system-arm".

>>  * and it's not going to be good for 64K pages on AArch64
>>    either (which I suspect will not be a rare choice)
>
> Does the kernel already use 64k pages for it's code?

There's a config option, which will cause it to use 64K
pages for everything including userspace.
(There's also 16K pages but I forget if Linux has support
for those.) I think the kernel can also use 64K pages in
some cases even in a 4K page config, but I don't know the
details.

thanks
-- PMM



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