wiki:DynamicByDefault

Version 11 (modified by igloo, 17 months ago) (diff)

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Dynamic by default

Performance

Full nofib results showing the effect of switching to dynamic-by-default are available for OS X 64bit, OS X 32bit, Linux 64bit and Linux 32bit. There is also a table of the highlights below. In summary:

Binary sizes are way down across the board, as we are now dynamically linking to the libraries.

Things are rosiest on OS X 64bit. On this platform, -fPIC is always on, so using dynamic libraries doesn't mean giving up a register for PIC. Overall, performance is a few percent better with dynamic by default.

On OS X 32bit, the situation is not so nice. On x86 we are very short on registers, and giving up another for PIC means we end up around 15% down on performance.

On Linux 64bit we have more registers, so the effect of giving one up for PIC isn't so pronounced, but we still lose a few percent performance overall.

For unknown reasons, 32bit Linux suffers even worse than 32bit OS X, with around a 30% performance penalty.

static -> dynamic
on OS X 64bit
static -> dynamic
on OS X 32bit
static -> dynamic
on Linux 64bit
static -> dynamic
on Linux 32bit
Binary Sizes
-1 s.d.-95.8%-95.8%-95.8%-95.9%
+1 s.d.-93.1%-92.8%-92.6%-92.4%
Average-94.6%-94.5%-94.5%-94.4%
Run Time
-1 s.d.-1.2%+11.7%-2.5%+16.6%
+1 s.d.+1.6%+20.0%+9.6%+40.3%
Average+0.2%+15.8%+3.3%+27.9%
Elapsed Time
-1 s.d.-6.9%+10.3%-2.5%+16.6%
+1 s.d.-0.3%+20.4%+9.6%+40.3%
Average-3.7%+15.2%+3.3%+27.9%
Mutator Time
-1 s.d.-1.3%+8.9%-5.0%+18.3%
+1 s.d.+1.9%+18.3%+7.5%+46.8%
Average+0.3%+13.5%+1.1%+31.8%
Mutator Elapsed Time
-1 s.d.-4.5%+7.7%-5.0%+18.3%
+1 s.d.+0.3%+18.8%+7.5%+46.8%
Average-2.1%+13.1%+1.1%+31.8%
GC Time
-1 s.d.-1.4%+16.3%+5.6%+13.4%
+1 s.d.+1.8%+27.1%+11.2%+24.0%
Average+0.2%+21.6%+8.4%+18.6%
GC Elapsed Time
-1 s.d.-1.5%+15.8%+5.6%+13.4%
+1 s.d.+1.3%+25.6%+11.2%+24.0%
Average-0.1%+20.6%+8.4%+18.6%
Compile Times
-1 s.d.-11.7%+6.2%-1.8%+27.0%
+1 s.d.-0.5%+18.2%+7.8%+37.8%
Average-6.3%+12.1%+2.9%+32.3%

OS X 32bit vs 64bit

Currently, some people use the 32bit version of GHC on OS X for performance reasons. It's not clear for how much longer this will be viable, as other OS X libraries start dropping 32bit support.

Full nofib results comparing the two are here for static by default, and here for dynamic by default, but the highlights are in the table below.

The left-hand column shows the status quo: 64bit only beats 32bit in mutator time, and that is a shallow victory as the higher GC time means that total runtime is worse for 64bit.

The right-hand column shows what the situation would be if we switch to dynamic instead. Allocations, memory use etc remain higher due to all word-sized things being twice as big. However, the speed difference moves in 64bit's favour, and 64bit is now faster overall.

x86 -> x86_64
when static by default
x86 -> x86_64
when dynamic by default
Binary Sizes
-1 s.d.+38.0%+7.4%
+1 s.d.+38.6%+30.6%
Average+38.3%+18.5%
Allocations
-1 s.d.+63.2%+63.2%
+1 s.d.+114.4%+114.4%
Average+87.0%+87.0%
Run Time
-1 s.d.-23.5%-31.6%
+1 s.d.+36.1%+14.7%
Average+2.1%-11.4%
Elapsed Time
-1 s.d.-18.2%-30.0%
+1 s.d.+40.1%+17.0%
Average+7.0%-9.5%
Mutator Time
-1 s.d.-32.4%-38.8%
+1 s.d.+20.1%+3.0%
Average-9.9%-20.6%
Mutator Elapsed Time
-1 s.d.-28.7%-37.9%
+1 s.d.+22.5%+4.4%
Average-6.6%-19.5%
GC Time
-1 s.d.+4.5%-11.9%
+1 s.d.+74.8%+54.1%
Average+35.2%+16.5%
GC Elapsed Time
-1 s.d.+7.9%-8.0%
+1 s.d.+75.1%+56.7%
Average+37.4%+20.0%
Total Memory in use
-1 s.d.-1.7%-1.9%
+1 s.d.+88.9%+88.9%
Average+36.3%+36.1%
Compile Times
-1 s.d.+11.9%-8.9%
+1 s.d.+21.1%+2.9%
Average+16.4%-3.1%