Re: [RFC PATCH 1/5] lguest: mmap backing file

Avi Kivity
2008-03-23T09:11:02Z

Anthony Liguori wrote:
>>>
>>>
>> If we're going to mod the kernel, how about a "mmap this part of their address
>> space" and having the kernel keep the mappings in sync. But I think that if
>> we want to get speed, we should probably be doing the copy between address
>> spaces in-kernel so we can do lightweight exits.
>>
>>
>
> I don't think lightweight exits help the situation very much. The
> difference between a light weight and heavy weight exit is only 3-4k
> cycles or so.
>

On what host cpu? IIRC the difference was bigger on Intel (and in
relative terms, set to increase).

> in-kernel doesn't make the situation much easier. You have to map pages
> in from a different task. It's a lot easier if you have both guest
> mapped in userspace.
>

The kernel already has everything mapped (kmap_atomic() is an addition
on x86_64).

--
error compiling committee.c: too many arguments to function

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