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[Bug fortran/78611] -march=native makes code 3x slower
- From: "pepalogik at seznam dot cz" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 30 Nov 2016 18:45:02 +0000
- Subject: [Bug fortran/78611] -march=native makes code 3x slower
- Auto-submitted: auto-generated
- References: <bug-78611-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78611
--- Comment #11 from Jan Lachnitt <pepalogik at seznam dot cz> ---
Thank you all for a rapid investigation of the problem.
Here is a confirmation with the large test case:
jenda@VivoBook ~/Bug reports/gfortran/6/PhSh1 $ gfortran-6 phsh1.f -std=legacy
-I. -march=core-avx-i -o core-avx-i/phsh1
jenda@VivoBook ~/Bug reports/gfortran/6/PhSh1 $ cd core-avx-i/
jenda@VivoBook ~/Bug reports/gfortran/6/PhSh1/core-avx-i $ time ./phsh1 <
../bmtz
Slab or Bulk calculation?
input 1 for Slab or 0 for Bulk
Input the MTZ value from the substrate calculation
real 221m0.225s
user 220m52.488s
sys 0m4.488s
jenda@VivoBook ~/Bug reports/gfortran/6/PhSh1/core-avx-i $ rm check.o mufftin.d
jenda@VivoBook ~/Bug reports/gfortran/6/PhSh1/core-avx-i $ LD_BIND_NOW=1 time
./phsh1 < ../bmtz
Slab or Bulk calculation?
input 1 for Slab or 0 for Bulk
Input the MTZ value from the substrate calculation
4512.06user 1.50system 1:15:16elapsed 99%CPU (0avgtext+0avgdata
7296maxresident)k
23408inputs+34424outputs (7major+1219minor)pagefaults 0swaps
Really, LD_BIND_NOW=1 does wonders :-) .
https://sourceware.org/bugzilla/show_bug.cgi?id=20495#c8 suggests building with
"-Wl,-z,now" (I suppose this does the same as LD_BIND_NOW=1). Can it be used as
a general workaround, before glibc 2.25 is available?