Re: [Qemu-devel] passing translated address out in QEMU

[Wei-Ren Chen]

> That might be difficult. what i did was that i disabled inlined
> translated and push the virt/phys address into 2 new fields in the cpu
> structure in the call out lookup. because in the callout lookup we
> have a handle to the cpu env.

  What you mean by "disabled inlined translated"? You mean apply Max's
patch so that all guest memory access go through the slow path without
looking software tlb? Since you said you're running arm on x86 host,
I guess what you did might be,

int cpu_arm_handle_mmu_fault (CPUARMState *env, target_ulong address,
                              int access_type, int mmu_idx)
{
    ...

    ret = get_phys_addr(env, address, access_type, is_user, &phys_addr, &prot,
                        &page_size);

    // store phys_addr into env->cpu_last_paddr

    ...
}
 
> not too sure how much impact inlined lookup has on the performance.
> since i disabled it, next step i would just get rid of that piece of
> generated assembly, as it is no good for icache ( generated for every
> memory operation).

  You can run a benchmark inside your guest. I guess if you run a
long-running benchmark, you can see performance degradation. If software
tlb hit, you can get the value of guest memory in the code cache
with a few host instructions. Disabling software tlb lookup, every guest
memory access will call a helper function which takes a lot of time.
What you mean by "get rid of that piece of generated assembly"?

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj