Re: [Qemu-devel] [PATCH 1/7] alpha: Implement IMB; add placeholders for other userspace PALcalls.

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Dec 13, 2009 at 11:54:02AM -0800, Richard Henderson wrote:
> On 12/13/2009 11:28 AM, Aurelien Jarno wrote:
> >Is it really necessary to flush all the TB here? QEMU should already
> >discard TB that have been modified.
> 
> No.  But I meant to look into this more carefully with a view to
> disabling the other checking within QEMU and speed things up a tad.
> It seems to me that the explicit checking with each memory write
> ought to only be necessary on architectures like x86 that don't
> architecturally require a flush insn to be used.

This is actually done only on the first write access to a page and not
to each write, so it should not be so costly. It is however something
to investigate, as I agree that removing the checks can add some 
speed-up.

> I can drop this fragment if necessary for patch acceptance, however.
> 

I think it is better to drop it until we have a better view of the whole
thing. You can add a comment saying that an optimisation might be
possible here. 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net