Date: Sun, 14 Sep 2008 22:39:40 -0400 From: "Josh Carroll" <josh.carroll@gmail.com> To: "Stephen Montgomery-Smith" <stephen@math.missouri.edu> Cc: freebsd-current@freebsd.org Subject: Re: Improved multiprocessor usage on amd64 Message-ID: <8cb6106e0809141939l99ebb62kea67172fe2fbd411@mail.gmail.com> In-Reply-To: <48CDBC78.4010409@math.missouri.edu> References: <48CDBC78.4010409@math.missouri.edu>
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On Sun, Sep 14, 2008 at 9:38 PM, Stephen Montgomery-Smith <stephen@math.missouri.edu> wrote: > I have a dual core amd64 on which I run a processor intensive numerical > program. I had been frustrated because it seemed to run 3 or 4 times faster > under Linux. But with a recent upgrade of FreeBSD-CURRENT, it now goes at > about the same speed as Linux. Which release/version were you running prior? Keep in mind, by default, various debugging knobs/etc are enabled in -current, so perhaps you went from a kernel with WITNESS/etc enabled to a kernel without these? I can run it here (on 7.1-PRERELEASE/amd64) if you'd like to send the source (to this address). > The program takes about an hour. For the first minute, the program runs > rather slowly, but then it is as if the operating system finds its way, and > suddenly it speeds up. "top -H" suggests that for the first minute that one > thread is going really slowly, and is perhaps being starved or something. Have you run a ktrace on it? That would be useful to see what's going on. > My question is - why is this happening, and is this something I should > expect? Are there certain switches or sysctls I can set to make it go fast > from the get go? Hard to say without seeing the code and knowing precisely what it does. Perhaps it's doing a lot of I/O up front or some preparations prior to the calculations? Regards, Josh
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