On Tue, Dec 24, 2024 at 11:52:38PM +0000, Pádraig Brady wrote:
However this is a regression on i7-5600U at least:
I'm seeing the same on older consumer hardware, even after the latest
patch (i3-6100):
$ time ./cksum --debug /tmp/testfil
cksum: avx512 support not detected
cksum: avx2 support not detected
cksum: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m27.717s
user 0m4.519s
sys 0m23.173s
$ time ./cksum_chorba --debug /tmp/testfil
cksum_chorba: avx512 support not detected
cksum_chorba: avx2 support not detected
cksum_chorba: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m31.288s
user 0m6.863s
sys 0m24.404s
on older server hardware (E3-1240 v5) I do see a slight improvement in
user time, but the system time increases and *not once* did I see the
overall runtime decrease (I did run them in the opposite order as well).
Maybe this indicates that the change trashes the cpu cache or somesuch?
$ time ./cksum --debug /tmp/testfil
cksum: avx512 support not detected
cksum: avx2 support not detected
cksum: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m22.923s
user 0m3.956s
sys 0m18.867s
$ time ./cksum_chorba --debug /tmp/testfil
cksum_chorba: avx512 support not detected
cksum_chorba: avx2 support not detected
cksum_chorba: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m23.962s
user 0m3.768s
sys 0m20.165s
$ time ./cksum_chorba --debug /tmp/testfil
cksum_chorba: avx512 support not detected
cksum_chorba: avx2 support not detected
cksum_chorba: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m25.021s
user 0m3.776s
sys 0m21.235s
$ time ./cksum --debug /tmp/testfil
cksum: avx512 support not detected
cksum: avx2 support not detected
cksum: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m23.961s
user 0m4.160s
sys 0m19.798s
on older AMD server hardware it's closer; just as on the intel hardware
there's a decrease in user time and an increase in system time, but the
results are close enough that it's a wash with sometimes one being
faster and somtimes the other:
$ time ./cksum_chorba --debug /tmp/testfil
cksum_chorba: avx512 support not detected
cksum_chorba: avx2 support not detected
cksum_chorba: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m14.509s
user 0m5.083s
sys 0m9.410s
$ time ./cksum --debug /tmp/testfil
cksum: avx512 support not detected
cksum: avx2 support not detected
cksum: using pclmul hardware support
3018728591 68719476736 /tmp/testfil
real 0m14.220s
user 0m5.626s
sys 0m8.578s
cf same binaries on zen4 (EPYC 9354P) where the new code is a clear
overall improvement:
$ time ./cksum --debug /tmp/testfil
cksum: using avx512 hardware support
3018728591 68719476736 /tmp/testfil
real 0m9.396s
user 0m1.720s
sys 0m7.676s
$ time ./cksum_chorba --debug /tmp/testfil
cksum_chorba: using avx512 hardware support
3018728591 68719476736 /tmp/testfil
real 0m8.769s
user 0m1.284s
sys 0m7.485s
