low(er) disk performance with sched_4bsd then with sched_ule

Andrew Gallatin gallatin at cs.duke.edu
Mon Sep 19 11:06:27 PDT 2005

Scott Long writes:
 > I don't know if it's the case here or not, but GCC now does very
 > aggressive function inlining, so much so that it's nearly impossible
 > to look at a backtrace and figure out what the actual call path was.
 > Compiling with -O instead of the -O2 default turns off this 'feature'
 > (and I use that term quite liberally), so it might be useful to
 > recompile there kernel with 'CFLAGS= -O' in /etc/make.conf and see
 > if it changes the profiling numbers at all.

If inlining were at fault,  I would expect to see something which
calls bcopy (copin/copyout or uiomove) have a lot of samples.

 > Also, I think that there was some talk last year about things like
 > preemption and fast interrupts screwing up certain kinds of profiling.
 > I don't recall if there was a solution to this, though.

I wonder if this could be it.  But I'm still not sure how they
could interfere with a copyin/copyout in a process context..


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