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

[Gary Benson <gbenson@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 1444 bytes --]

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/

[-- Attachment #2: profile --]
[-- Type: text/plain, Size: 1334 bytes --]

samples  %        image name     symbol name
-------------------------------------------------------------------------
347937   11.4258  no-vmlinux     /no-vmlinux
317639   10.4309  libc-2.13.so   __memcpy_sse2
231494    7.6020  gdb            lookup_minimal_symbol_text
230405    7.5662  gdb            objfile_data
206993    6.7974  libc-2.13.so   __GI_memset
169853    5.5778  gdb            svr4_same
154056    5.0590  gdb            lookup_minimal_symbol
105589    3.4674  libc-2.13.so   _int_free
99916     3.2811  gdb            solib_add
93557     3.0723  libc-2.13.so   _int_malloc
78125     2.5655  gdb            namespace_update_incremental
74170     2.4357  gdb            create_longjmp_master_breakpoint
70165     2.3041  libc-2.13.so   __strcmp_sse2
62896     2.0654  gdb            lookup_minimal_symbol_and_objfile
55876     1.8349  gdb            create_overlay_event_breakpoint
51030     1.6758  gdb            get_objfile_arch
46512     1.5274  gdb            create_exception_master_breakpoint
45851     1.5057  gdb            create_std_terminate_master_breakpoint
40766     1.3387  ld-2.16.90.so  _dl_name_match_p
40233     1.3212  gdb            allocate_objfile
34723     1.1403  ld-2.16.90.so  _dl_map_object_from_fd
33676     1.1059  libc-2.13.so   freehook
31009     1.0183  ld-2.16.90.so  _dl_map_object