This is results of simple CFLAGS test. Maybe it will be useful for someone so
I post it here. I was wonder if results for old processors will be same as for
the fast ones so I made this simple test.
You can compare this test with Javier Villavicencio's
(http://article.gmane.org/gmane.linux.gentoo.user/51881)).

I was compiling gnuchess (http://www.gnu.org/software/chess/chess.html) with
various CFLAGS settings. For each compiled gnuchess I ran these commands:

./gnuchess
depth 8
go
quit

and wrote down duration of "go" command (gnuchess prints it). Following numbers
are average values of five (or more) values.

Each test was performed two times. One in X with many processes running
(mostly sleeping). Second in console with minimum of processes and with niced
priority (nice -18) of gnuchess.

Values are in seconds. In parentheses is place (best is on 1st place, worst on
14th place). Lines marked with "X" are values from test in X environment and
"C" lines are values from console test.

Here are the results:

 1. Without optimizations
  X 22.12 (14)
  C 17.65 (14)
  [slowest of course - 14th place]

 2. "Basic" O2 test
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2 -fomit-frame-pointer):
  X 16.73 (8, 9)
  C 13.29 (6)
  [much better]

 3. Changed to O3
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O3 -fomit-frame-pointer):
  X 17.23 (12)
  C 15.25 (13)
  [slower than O2 - same result as in Javier Villavicencio's test]

 4. Trying O3 being faster
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O3 -fomit-frame-pointer
    -falign-functions=4 -falign-jumps=4):
  X 16.62 (7)
  C 13.50 (7)
  [almost same as "basic" O2]

 5. Don't give up with O3
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O3 -fomit-frame-pointer
    -falign-functions=4 -falign-jumps=4
    -fforce-addr):
  X 17.09 (11)
  C 14.39 (12)
  [bad results ]

 6. Piece of O3 in O2 (O3 implies -frename-registers)
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2 -fomit-frame-pointer
    -frename-registers):
  X 16.44 (4)
  C 13.19 (5)
  [pretty fast - as in Javier Villavicencio's test]

 7. Trying somethin else
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2 -fomit-frame-pointer 
    -falign-functions=4 -falign-jumps=4):
  X 16.25 (1)
  C 13.11 (3, 4)
  [bingo! first place in X environment; also close to second and first place in
   console]

 8. Combination of two previous
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2 -fomit-frame-pointer
    -frename-registers
    -falign-functions=4 -falign-jumps=4):
  X 16.73 (8, 9)
  C 14.03 (10)
  [aargh! slow; why???]

 9. Trying -fforce-addr
   (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2 -fomit-frame-pointer
    -fforce-addr):
  X 18.33 (13)
  C 13.74 (9)
  [slower - like with O3; Javier Villavicencio's test shows same results;
   this is much slower in X (almost last place) - why?]

10. Just for a record
  (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2 -fomit-frame-pointer
   -fforce-addr
   -frename-registers):
  X 17.02 (10)
  C 13.51 (8)
  [little bit faster]

11. Let's see "clean" O2
  (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -O2):
  X 16.58 (6)
  C 14.14 (11)
  [much slower in console (11th place)]

12. And "clean" Os
  (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -Os):
  X 16.28 (2)
  C 13.11 (3, 4)
  [great! I didn't expect this]

13. Let's play with Os
  (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -Os -fomit-frame-pointer):
  X 16.49 (5)
  C 13.03 (2)
  [hmm, strange - faster in console and slower in X]

14. Go Os Go!
  (-mcpu=pentium-mmx -march=pentium-mmx -mmmx -Os -fomit-frame-pointer
   -falign-functions=4 -falign-jumps=4):
  X 16.31 (3)
  C 12.99 (1)
  [fastest in console! very close to first and second place in X; this is
   different result than Bill Kenworthy got
   (see http://article.gmane.org/gmane.linux.gentoo.user/50998)]

Note that this test is specific to one task in one application. Effect can be
different for whole system (see different effects of some options when
application is running in X (system with many processes) and in console
(minimum processes)).

Machine specs:

$ uname -rmip
2.4.20-gentoo-r7 i586 Pentium MMX GenuineIntel

Kernel is compiled with preemptive multitasking.

Processor: Pentium 166 MMX, RAM: 64MB

Robert.

-- 
Robert Cernansky
E-mail: hslists <at> zoznam.sk
Jabber: HS <at> jabber.sk

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