Re: [User-mode-linux-devel] Performance enhancement idea...

[Chris L. <sa...@sk...>]

The only problem is that you only have two bytes of code space to work
with (int 0x80 is encoded as 0xCD 0x80), and a call takes 5? bytes...

:(  If there is any other useful thing to fit into two bytes... that would
be cool too!  

-Chris


On Fri, 7 Jul 2000, Jose Renau wrote:

> 
>  If the idea is to increase the performance, why not no change the "int
> $80" for a "call um_syscall". um_syscall can "communicate" when it's
> strictly necessary. For example, a getpid could be done locally.
> 
>  This optimization could do te umlinux even faster than the "default"
> Linux.
> 
>  Suggestions?
> 
> On Fri, 7 Jul 2000, Chris Lattner wrote:
> 
> > Currently, syscall entry requires the tracing thread to wake up, munge the
> > registers around, and do other stuff before the syscall'ing thread
> > continues in the kernel...  I have two ideas to improve syscall
> > performance:
> > 
> > 1. Instead of changing EAX to make the syscall do a getpid, why not just
> > add 2 to the EIP to skip over the int 80?
> > 2. Additionally, why not change that int 80 to be "ud2" or some other
> > opcode that will cause a SIGILL?  When receiving a sigill, just check for
> > the magic opcode and if it is set, do the syscall... this would have the
> > advantage that the ptrace/c-switch overhead would be reduced...
> > 
> > Does anyone see any problems with these suggestions?  I may be interested
> > in implementing them if not...
> > 
> > -Chris
> > 
> > 
> > 
> > _______________________________________________
> > User-mode-linux-devel mailing list
> > Use...@li...
> > http://lists.sourceforge.net/mailman/listinfo/user-mode-linux-devel
> > 
> 
> -------------------------------------------------------------------
>  Jose Renau Ardevol        | The great things in life are what they
>             re...@ui... |  seem to be.           Oscar Wilde
> -------------------------------------------------------------------
> 
> 
> _______________________________________________
> User-mode-linux-devel mailing list
> Use...@li...
> http://lists.sourceforge.net/mailman/listinfo/user-mode-linux-devel
>