Re: [Qemu-devel] qemu dynamic translation (system design) question

Re: [Qemu-devel] qemu dynamic translation (system design) question

[Laurent DESNOGUES]

> b. Once a block is generated some ID should be assigned to it right ?
> in which src file it is stored ?
> c. The next time a src block with the same signature is encountered
> the cached host binary is used right ?  -- How does qemu detect that
> is the same guest block ? md5sum or other fingerprinting methods ?

Look in qemu-exec.c/tb_find_fast


Laurent

Re: [Qemu-devel] qemu dynamic translation (system design) question

[S.P.T.Krishnan]

Hi Laurent,

Thanks for the direction.

I am just thinking.  If I run a guest OS once and observe the blocks
that are translated and may be reused.  Then I again re-run the OS,
can I expect the same blocks are translated ?  i.e., is qemu
consistent on how it partitions the asm into blocks on successive runs
or the guest OS ?

Note: in both cases the user doesn't interact with the Guest OS.  It
is up for, say 1 min and then shutdown in both runs.

regards,
Krishnan

On 8/19/06, Laurent DESNOGUES <laurent.desnogues@wanadoo.fr> wrote:
> > b. Once a block is generated some ID should be assigned to it right ?
> > in which src file it is stored ?
> > c. The next time a src block with the same signature is encountered
> > the cached host binary is used right ?  -- How does qemu detect that
> > is the same guest block ? md5sum or other fingerprinting methods ?
>
> Look in qemu-exec.c/tb_find_fast
>
>
> Laurent
>
>
> _______________________________________________
> Qemu-devel mailing list
> Qemu-devel@nongnu.org
> http://lists.nongnu.org/mailman/listinfo/qemu-devel
>

Re[2]: [Qemu-devel] qemu dynamic translation (system design) question

[Paul Sokolovsky]

Hello S.P.T.Krishnan,

Sunday, August 20, 2006, 6:23:11 PM, you wrote:

> Hi Laurent,

> Thanks for the direction.

> I am just thinking.  If I run a guest OS once and observe the blocks
> that are translated and may be reused.  Then I again re-run the OS,
> can I expect the same blocks are translated ?  i.e., is qemu
> consistent on how it partitions the asm into blocks on successive runs
> or the guest OS ?

> Note: in both cases the user doesn't interact with the Guest OS.  It
> is up for, say 1 min and then shutdown in both runs.

  My 2 cents of pure scholastic reasoning:
  
  Let's assume that QEMU uses deterministic rules for block
translation. Then, it just translates what CPU goes thru. Does any
contemporary OS leads CPU in deterministic ways? No. It largely
depends on various environment parameters, of which user interaction
is not the last. There're interrupts occuring in rather random places
with respect to mainline execution, I/O delays, etc. As these
parameters in guest OS depend on QEMU's interaction with host OS, they
are not deterministic in it either. Well, but does QEMU's translation
itself deterministic? Not really, as it uses caches, and thus depend on
memory parameters in host OS.

> regards,
> Krishnan


-- 
Best regards,
 Paul                            mailto:pmiscml@gmail.com