On 2017.05.25 at 11:55 +0200, Martin Liška wrote:
> Hi.
>
> As I spoke about the PGO with Honza and Richi, current 3-stage is not ideal
> for following
> 2 reasons:
>
> 1) stageprofile compiler is train just on libraries that are built during
> stage2
> 2) apart from that, as the compiler is also used to build the final compiler,
> profile
> is being updated during the build. So the stage2 compiler is making different
> decisions.
>
> Both problems can be resolved by adding another step in between current
> stage2 and stage3
> where we train stage2 compiler by building compiler with default options.
>
> I'm going to do some measurements.
I did some measurements on gcc67 (trunk with --enable-checking=release).
The apparent speedup is in the noise.
Without your patch:
Performance counter stats for 'g++ -w -Ofast tramp3d-v4.cpp' (10 runs):
15749.058451 task-clock (msec) # 0.997 CPUs utilized
( +- 0.13% )
1,352 context-switches # 0.086 K/sec
( +- 0.16% )
7 cpu-migrations # 0.000 K/sec
( +- 5.73% )
269,142 page-faults # 0.017 M/sec
( +- 0.01% )
60,676,581,181 cycles # 3.853 GHz
( +- 0.09% ) (83.35%)
13,401,784,189 stalled-cycles-frontend # 22.09% frontend cycles
idle ( +- 0.20% ) (83.33%)
12,926,843,370 stalled-cycles-backend # 21.30% backend cycles
idle ( +- 0.04% ) (83.31%)
73,074,099,356 instructions # 1.20 insn per cycle
# 0.18 stalled cycles per
insn ( +- 0.02% ) (83.34%)
16,607,220,814 branches # 1054.490 M/sec
( +- 0.03% ) (83.36%)
616,673,310 branch-misses # 3.71% of all branches
( +- 0.08% ) (83.36%)
15.803602619 seconds time elapsed
( +- 0.14% )
With your patch:
Performance counter stats for 'g++ -w -Ofast tramp3d-v4.cpp' (10 runs):
15735.220610 task-clock (msec) # 0.997 CPUs utilized
( +- 0.11% )
1,354 context-switches # 0.086 K/sec
( +- 0.22% )
6 cpu-migrations # 0.000 K/sec
( +- 6.67% )
269,164 page-faults # 0.017 M/sec
( +- 0.01% )
60,723,862,242 cycles # 3.859 GHz
( +- 0.08% ) (83.35%)
13,382,554,421 stalled-cycles-frontend # 22.04% frontend cycles
idle ( +- 0.14% ) (83.31%)
12,912,171,664 stalled-cycles-backend # 21.26% backend cycles
idle ( +- 0.03% ) (83.34%)
73,109,081,227 instructions # 1.20 insn per cycle
# 0.18 stalled cycles per
insn ( +- 0.03% ) (83.34%)
16,590,421,798 branches # 1054.349 M/sec
( +- 0.02% ) (83.35%)
616,669,135 branch-misses # 3.72% of all branches
( +- 0.08% ) (83.36%)
15.788772466 seconds time elapsed
( +- 0.12% )
--
Markus
