[Qemu-devel] Re: [PATCH] CONFIG_MMU_MAP powerpc host support

[Piotras <piotras@gmail.com>]

Great!

Do you have an estimate of possible performance gain by introducing 
direct pointer to mmu_map for memory read?

I have two ideas for future experimentation.

There is a trick possible without wasting another register for global 
variable: use two copies of CPUState (one for privileged and another 
for user mode), then make mmu_map.add_read first member of the 
struct. This would introduce guest register coping for user/supervisor 
switch, but maybe performance gain would justify this.

Another idea: if we could align add_read/add_write on 64k boundary, 
"addi" could be removed.


Regards,

Piotrek

On Mon, 20 Dec 2004 18:55:21 +0100, Magnus Damm <magnus.damm@gmail.com> wrote:
> Hello,
> 
> This patch adds powerpc host support to the CONFIG_MMU_MAP patch
> written by Piotrek. My patch should be applied on top of
> v1-part[1-3].patch.gz. I have only tested the code with a x86 guest on
> a ppc host running Linux - someone, please test on a host running OSX.
> 
> Performance gain reported by nbench:
> 
> Memory index: 50%
> Integer index: 44%
> Fp index: 4%
> 
> Right now each map-memory access consists of 5-6 powerpc instructions.
> If a direct pointer to mem_map could be kept in a register then we
> would be down to 3-4 instructions per memoy access...
> 
> / magnus