https://bugzilla.novell.com/show_bug.cgi?id=811546 https://bugzilla.novell.com/show_bug.cgi?id=811546#c0 Summary: Executables compiled with g++ run twice slower in opensuse 12.3 than in 12.2 Classification: openSUSE Product: openSUSE 12.3 Version: Final Platform: x86-64 OS/Version: SUSE Other Status: NEW Severity: Normal Priority: P5 - None Component: Development AssignedTo: bnc-team-screening@forge.provo.novell.com ReportedBy: j9002j@yahoo.com QAContact: qa-bugs@suse.de Found By: --- Blocker: --- User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:19.0) Gecko/20100101 Firefox/19.0 Once you write a simple C++ source file that does math computations with math functions sin(), cos(), exp(), rand(), and compile it in opensuse 12.3 64 bit, you discover that it runs twice (!) slower than in opensuse 12.2 64 bit. Same is true for at least one large program. Versions of compiler and kernel: OLD: gcc version 4.7.1 20120723 [gcc-4_7-branch revision 189773] (SUSE Linux) 3.4.33-2.24-desktop #1 SMP PREEMPT Tue Feb 26 03:34:33 UTC 2013 (5f00a32) x86_64 x86_64 x86_64 GNU/Linux NEW: gcc version 4.7.2 20130108 [gcc-4_7-branch revision 195012] (SUSE Linux) 3.7.10-1.1-desktop #1 SMP PREEMPT Thu Feb 28 15:06:29 UTC 2013 (82d3f21) x86_64 x86_64 x86_64 GNU/Linux See http://forums.opensuse.org/english/other-forums/development/programming-scri... Compilation is done with option -O2. Reproducible: Always Steps to Reproduce: 1. Use desktop PCs with Intel Core i7 family processors. 2. Write C++ code that will do computations. 3. Compile in opensuse 12.2 and 12.3 with and without optimization options. 4. Measure speed of execution in both OSes in single-threaded run. Actual Results: With optimization, in opensuse 12.3, one iteration of outermost loop takes about 6 s. In opensuse 12.2, same takes about 3 s. Without optimization, the numbers are twice larger. Executable compiled in opensuse 12.2 and run in opensuse 12.3 also runs twice slower than in opensuse 12.2. Expected Results: Expected about the same time per loop iteration, or slightly better results for opensuse 12.3. The problem of speed degradation does not show up in small laptops with weak processors. It looks like large-scale RAM operations are not slowed down. One needs a set of computers with different configurations and OSes to pin down the root cause. Perhaps in Ubuntu the slowdown will not be observed when using gcc 4.7.2. -- Configure bugmail: https://bugzilla.novell.com/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug.