Re: [Qemu-devel] [RFC] Host vs Guest memory allocation

[Avi Kivity <avi@redhat.com>]

On 04/06/2010 02:18 AM, Aurelien Jarno wrote:
>
>> (1) Enable softmmu for userland. This is of course the highest overhead,
>>      but will work for all combinations.
>>
>>      
> This option would solve a lot of problems and simplify a lot of code:
> unaligned access on hosts requiring strict alignements, different page
> size between host and guest, self-modifying code, 64-bit user land on
> 32-bit host, etc... That's what currently comes to my mind, but that
> would solve a lot more problems.
>
> It will clearly have a high overhead, but it might be interesting to
> quantify it, to see if we should continue to add tons of code/workaround
> to linux-user instead of switching to softmmu for userland. It could
> also be optimized, for example by increasing the TLB size compared to
> system mode, and doing TLB preallocation on mmap calls.
>
>    

You could reduce the overhead somewhat by using kvm for memory 
translation on hosts that support it.  Of course tcg translation and 
syscall costs will grow by the exit overhead.


-- 
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