Re: [RFA 5/4 take 2] Improved linker-debugger interface

[Gary Benson <gbenson at redhat dot com>]

André Pönitz wrote:
> On Thu, Jul 19, 2012 at 04:19:13PM +0100, Gary Benson wrote:
> > Attached is a patch to avoid calling update_section_map from the
> > probes interface.  Updated timings are as follows:
> > 
> >   no of solibs    100     250     500     1000    2000    5000
> >   ------------------------------------------------------------
> >   old interface     1       3       9       35     141     942
> >   new interface     0       0       1        4      14      89
> >   (times in seconds)
> > 
> > So, with this patch GDB is not three but ten times faster.
> 
> It pretty much looks like there is still some quadratic behaviour
> somewhere...

Yes.  It's difficult to avoid given the current architecture.
target_so_ops->current_sos() is expected to return a freshly
allocated list of libraries to update_solib_list(), and the
latter is expected to free them.  This makes sense for the
standard interface, which reads everything from the inferior
into a list and returns it.  The probes interface already has
everything read by the time target_so_ops->current_sos() is
called, but it can't just return its own copy because the
rest of GDB will start freeing bits of it, so it needs to
copy it.  Every time a library is loaded, a new copy of the
list is made, but every time a library is loaded the list is
one element bigger.  You can see all the memcpy calls in the
profile I attached.

Cheers,
Gary

-- 
http://gbenson.net/

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