https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81828
Bug ID: 81828
Summary: Cilkplus performance regression on ARM...
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ejolson at unr dot edu
Target Milestone: ---
Created attachment 41979
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41979&action=edit
Graph showing performance regression...
Code for gcc version 7.1 using Cilkplus parallel programming extensions on ARM
is running much slower than the same code with version 6.2. Details may by
viewed graphically as
http://fractal.math.unr.edu/~ejolson/bench/dotprod/gcc71-8.png
which consistently shows a loss of performance using any combination of 1 to 8
cores on a Samsung/Nexell S5P6818 based SBC. More information and example code
is available at
https://www.raspberrypi.org/forums/viewtopic.php?p=711196#p1197225
My impression is that this regression affects almost all Cilkplus code on ARM
and is possibly the result unaligned cactus stack additional overhead in
switching tasks that was not present in the 6.2 version. It is likely that
performance-based tests for ARM Cilkplus are needed to insure such regressions
do not happen in the future. Note that the performance of serial code is not
affected.
The test code was compiled for 32-bit mode using options
-fcilkplus -O3 -mcpu=cortex-a7 -mfpu=neon-vfpv4 -mfloat-abi=hard
-ffast-math
and run under identical circumstances in both cases.
