Karsten Wiese wrote:
Am Montag, 8. August 2005 13:19 schrieb Alexander Nyberg:
There are many places where one could replace run-time tests with
#ifdef's but it makes reading more difficult (and in longer terms
maintainence). Have you benchmarked any workload that benefits
from this?
Performance gain is small, but measurable: 0,02%
Tested on an Atlon64 running at 1000MHz.
I took this value from 9 runs (each with/without the patch) of
$ time lame x.wav
where each took about 1 minute.
3000 Interrupts/s were generated at the time by running
$ jackd -R -dalsa -p64 -n2
0,02% really isn't that much....but Athlon64 is better than P4
with branch predictions, I think.
Erm... ok, I won't insist on having this patch applied ;-)
Karsten
Removing dead code is always good - 0.02% is small, but if 100 kernel
developers all did the same, that adds up to 2% rather quickly, and that
is nothing to sneeze at. I like your patch, but you should add some
comments for maintainability about what CHECK_IRQ_PER_CPU does - see
include/asm-generic/pgtable.h for similar styling. If also probably
doesn't hurt to leave IRQ_PER_CPU defined even when
ARCH_HAS_CHECK_IRQ_PER_CPU is not, since it looks cleaner and prevents
future collisions with bits defined inside of an #ifdef.
Zach
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