Support for malign-double?
Fri Aug 21 23:01:00 GMT 1998
Thank you very much for your comments.
; In a message dated 8/20/98 4:13:18 PM Pacific Daylight Time,
; firstname.lastname@example.org writes:
; > linux performance is
; > about 20% better for floating point intensive application.
; You'd have to study harder than I'm willing to do to figure out which
; alignments are controlled by -malign-double, which are at the discretion of
; the OS or the math library, and which are controlled by the compiler in which
; version. It appears that linux-gnulibc1 aligns many local variables,
; including register spills, which cygwin32 does not. One of the effects I have
; observed is that -Os may be faster than -O2 on a P-Pro running certain code on
; cygwin32, where the two are about equal on a P2 on cygwin32, and -O2 may be
; faster on linux. My conclusion is that -O2 spills more registers, which are
; stored with unpredictable alignment in cygwin32.
; You must be running a P-Pro; data mis-alignment on the P-Pro can slow it down
; by a factor of 2 or 3 when there are L1 data cache misses, while I've
It is a PentiumII..
; been able to slow the P2 down by more than 50% for data cache misses. But,
; since you mention 20%, that's a typical penalty on the P2 for failing to use
; the p2align feature of current egcs. That, however, is the same on linux or
; cygwin32, if you install the same compiler and gas on each.
Both are from (egcs-1.0.2 release)...
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