Re: [uml-devel] Explaination of system call function flow in TT mode

[Blaisorblade <blaisorblade@yahoo.it>]

On Wednesday 18 May 2005 17:20, Bodo Stroesser wrote:
> Jeff Dike wrote:
> > On Wed, May 18, 2005 at 11:47:23AM +0200, Bodo Stroesser wrote:
> >>I also thought about not saving FP-regs on each kernel entry. But if you
> >> do this optimization, you need to save / restore FP-regs on switch_to.
> >> Also you need to get the FP-regs when setting up a signal-handler
> >> stackframe. And they
> >>have to be restored on sys_(rt_)sigreturn from the values found in the
> >>stackframe.
> >
> > True, but these are much less frequent than kernel entries/exits.
>
> Yes, so it makes sense to optimize this for i386 and x86_64.
>
> On s390, I'm not sure, what to do. Using s390's PTRACE_PEEK/POKEUSR_AREA
> UML can read or write all regs including FP in a single ptrace call.
> So, the change would speed up that call a bit, but would that be enough
> to pay the cost of additional ptrace calls in switch_to or signal handling?
I think no, because doing a syscall is probably more costly than copying some 
bytes, however it depends on the relative frequency. Doing a benchmark would 
probably be the better thing to do.
-- 
Paolo Giarrusso, aka Blaisorblade
Skype user "PaoloGiarrusso"
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade




-------------------------------------------------------
This SF.Net email is sponsored by Oracle Space Sweepstakes
Want to be the first software developer in space?
Enter now for the Oracle Space Sweepstakes!
http://ads.osdn.com/?ad_id=7412&alloc_id=16344&op=click
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel