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[Bug c++/53292] multi-threaded (OpenMP) is slower than single-threaded
- From: "jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 09 May 2012 13:29:00 +0000
- Subject: [Bug c++/53292] multi-threaded (OpenMP) is slower than single-threaded
- Auto-submitted: auto-generated
- References: <bug-53292-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53292
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-05-09 13:29:00 UTC ---
Sorry, missed you aren't measuring it with the single-threaded loop. Anyway,
the test is still not relevant, it is purely memory bound, and as you can see
from running it with very small arguments, the thread creation and omp for
initial overhead is in the noise, what you see is just how the cache hierarchy
of your CPU works. The inner loop in which all the measured time is spent in
is very similar (and even if hand edited to be identical it doesn't help at
all).