Re: more on gdb server

[Daniel Jacobowitz <dmj+ at andrew dot cmu dot edu>]

On Wed, Jul 18, 2001 at 03:40:57PM -0400, Quality Quorum wrote:
> On 18 Jul 2001, J.T. Conklin wrote:
> 
> > > > I know HP were once playing with ideas that would have eliminated any 
> > > > copying because they were finding memory read/write performance using 
> > > > ptrace (or what ever) lacking.
> > > 
> > > I would suppose they had something truly unusual - debuggin is going with 
> > > the pace of human reaction to debugging events and I can hardly imagine
> > > that network performance over local loop interface would be a factor here.
> > 
> > Remember that GDB may be issuing many low level commands for each high
> > level (CLI) command.  For example, a single step or next command may
> > issue several step instruction, fetch registers, and store registers
> > commands.  On some large programs, some interactive commands are
> > beyond the interactive threshold (something like .3 seconds?  I can't
> > remember the commonly quoted figure), this additional overhead would
> > only make it worse.
> > 
> > Also note that oftentimes it's not a human driving the debugging
> > session, but user defined functions that grovel through data
> > structures, call inferior functions, etc.
> 
> I still have hard time to beleive that there is an issue here.

Consider software watchpoints, already almost uselessly slow.  Consider
single-stepping over a single line of code consisting of forty or four
hundred machine instructions.  There can be a significant overhead.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer