2008/11/17 H. Peter Anvin <hpa@xxxxxxxxx>:
> Igor Podlesny wrote:
>>
[...]
>> Has anyone on the list similar observations? Can gcc's version
>> difference affect so much? I doubt that, but I can try build x86_32
>> with gcc 4.3.1 (as x86_64 was).
>>
>
> The SSE modes have nicer cache behaviours and are therefore preferred
> even if they are slower.
>
That was my guess that they're preferable (but I wasn't aware of exact
reason, thanks!). :-)
>
> It is very odd that your SSE2 modes are that much slower in 64-bit mode.
> It could just be an artifact of the may the test is done (cache
> anomalies?), but I kind of suspect there is something more fishy going on.
I've built gcc-4.2.4 and recompiled the kernel with it. .config's diff:
-CONFIG_LOCALVERSION="-64_1khz"
+CONFIG_LOCALVERSION="-64_1khz-gcc42"
CONFIG_LOCALVERSION_AUTO=y
CONFIG_SWAP=y
CONFIG_SYSVIPC=y
@@ -287,7 +287,7 @@
# CONFIG_RELOCATABLE is not set
CONFIG_PHYSICAL_ALIGN=0x200000
CONFIG_HOTPLUG_CPU=y
-CONFIG_COMPAT_VDSO=y
+# CONFIG_COMPAT_VDSO is not set
And dmesg now says:
[ 2.606258] raid6: int64x1 2210 MB/s
[ 2.623255] raid6: int64x2 3246 MB/s
[ 2.640257] raid6: int64x4 3289 MB/s
[ 2.657262] raid6: int64x8 3019 MB/s
[ 2.674262] raid6: sse2x1 4253 MB/s
[ 2.691258] raid6: sse2x2 5621 MB/s
[ 2.708261] raid6: sse2x4 5718 MB/s
[ 2.708299] raid6: using algorithm sse2x4 (5718 MB/s)
So, I deem that's not VDSO's effect but gcc's version instead.
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