On 2020-03-08 18:24, Jan Engelhardt wrote:
On Saturday 2020-03-07 23:16, Frans de Boer wrote:
I noticed that when I compile boinc, it is always
around 4x slower on the CPU
benchmarks then the version distributed by Tumbleweed. I do use '-O3
-funroll-loops -ffast-math' as specified on the boinc website.
blindly grab something from the manpage without
understanding - and conveying to subsequent readers - the implications?
"This option makes code larger, and may or may not make it run
(It does not say it explicitly, but "larger" leads to "slower" at a
Yes, after a certain point the benefit of using sequential code can be
negative if - for instance - the code runs out the cache, requiring
additional memory fetches. And no, it was a man page, but a page on the
boinc site itself as well as discussions on various fora.
Note that -ffast-math is even inserted automatically by the build system
of boinc itself. Apparently, they do not care so much about precision.
Then again, it is only boinc itself and does not affect the external tasks.
But to be sure, I tested various configurations and found that both
options do nothing to the issue. In fact, after experimenting with
various other benchmark tools, I see a difference of aprox. 7% between
two systems. Using the CPU benchmark from the TW boinc distribution, the
difference on one machine is 3,8x (AMD) and the other 6,3x (Intel) as
compared with the self compiled programs. So, what did the openSUSE team
did to get these benchmark results which do not reflect the real world
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