Date: Thu, 27 Feb 2014 20:23:47 -0700 From: Ian Lepore <ian@FreeBSD.org> To: freebsd-arm <freebsd-arm@FreeBSD.org> Subject: wandboard / imx6 hard float Message-ID: <1393557827.1149.117.camel@revolution.hippie.lan>
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After some testing last week I determined that hard float works on imx6,
so I enabled it (added option VFP) in the kernel configs. To check
whether it's enabled, see if "sysctl hw.floatingpoint" is set to 1.
To actually use the hardware floating point you have to add some options
to CFLAGS:
* For clang CFLAGS="-mfloat-abi=softfp"
* For gcc CFLAGS="-mfloat-abi=softfp -mfpu=vfp"
* You can do that on the make command line, in the environment, or
in /etc/make.conf.
I think the implication of float-abi=softfp is that floating point
arguments are passed in integer registers, and we're losing some
performance with that. But as I vaguely understand it, we're still
missing some piece of support code to enable full eabihf. Maybe
somebody who knows the status of that can fill in my hand-wavy blanks.
Hardware floating point makes a huge performance difference in apps that
use floating point. Using the venerable benchmarks/flops program from
ports, here's the results on my Wandboard quad running @ 984 MHz...
-------------------------------------------------------
FLOPS C Program (Double Precision), V2.0 18 Dec 1992
Module Error RunTime MFLOPS
(usec)
1 -1.5632e-13 3.0377 4.6087
2 -1.0347e-13 1.8709 3.7416
3 -3.1197e-14 3.1652 5.3709
4 7.7938e-14 2.7834 5.3890
5 -3.2641e-14 6.2713 4.6243
6 -9.9920e-16 5.4799 5.2920
7 -5.5650e-11 4.0721 2.9469
8 2.7700e-14 5.7273 5.2381
Iterations = 8000000
NullTime (usec) = 0.0000
MFLOPS(1) = 4.1535
MFLOPS(2) = 4.1052
MFLOPS(3) = 4.7811
MFLOPS(4) = 5.3043
-------------------------------------------------------
FLOPS C Program (Double Precision), V2.0 18 Dec 1992
Module Error RunTime MFLOPS
(usec)
1 -7.6739e-13 0.1058 132.2879
2 -5.7021e-13 0.0621 112.7249
3 -2.4314e-14 0.0967 175.8202
4 6.8501e-14 0.0875 171.3418
5 -1.6320e-14 0.1924 150.7668
6 1.3961e-13 0.1730 167.6504
7 -3.6152e-11 0.1160 103.4433
8 9.0483e-15 0.1771 169.3994
Iterations = 256000000
NullTime (usec) = 0.0081
MFLOPS(1) = 127.7076
MFLOPS(2) = 135.7852
MFLOPS(3) = 153.9281
MFLOPS(4) = 170.3133
------------------------------------------------------
-- Ian
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