Date: Mon, 19 Sep 2005 14:06:15 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Scott Long <scottl@samsco.org> Cc: current@freebsd.org Subject: Re: low(er) disk performance with sched_4bsd then with sched_ule Message-ID: <17198.65047.682527.433172@grasshopper.cs.duke.edu> In-Reply-To: <432CCEF5.2050608@samsco.org> References: <20050914194612.15692485.lehmann@ans-netz.de> <20050914222013.178dc4dc.lehmann@ans-netz.de> <84dead72050914135239514c49@mail.gmail.com> <20050915000053.448f251b.lehmann@ans-netz.de> <84dead7205091500152a7c25d1@mail.gmail.com> <20050915172005.072f4bdf.lehmann@ans-netz.de> <20050915181238.54b16b4b.lehmann@ans-netz.de> <84dead720509160921732e7f96@mail.gmail.com> <20050916184911.38e2739a.lehmann@ans-netz.de> <20050916225219.73b53cd0.lehmann@ans-netz.de> <84dead7205091619435c12b528@mail.gmail.com> <20050917102846.7bf26a56.lehmann@ans-netz.de> <17196.35762.395155.325627@grasshopper.cs.duke.edu> <432CCEF5.2050608@samsco.org>
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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.. Drew
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