Re: AMD64 much slower than i386 on FreeBSD 5.4-pre

From: jason henson (jason_at_ec.rr.com)
Date: 03/24/05

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    Date: Thu, 24 Mar 2005 00:57:58 -0500
To: em1897@aol.com

    em1897@aol.com wrote:

    >
    >
    >> The answer, Boris, is that the "team" has no idea what
    >> they're doing. Check out some of the threads on
    >> performance testing. They tune little pieces here
    >> and there, and break 10 other things in the process.
    >> Matt Dillon "determined" that 10,000 ints/second
    >> was "optimal". Of course if you're passing 10Kpps
    >> that means you get an interrupt for every
    >> packet.
    >>
    >> They're playing pin the tail on the donkey.
    >>
    >
    > You could understand what he was saying? I wanted to help but was
    > unsure of what he was asking. I also seem to remember that discussion
    > you are referring too. IIRC, 10,000hz for pooling was the setting they
    > ere talking about. But on it would very a little, and with the fxp
    > based card polling hurt a little because the card was already ding its
    > own thing in hardware. So that setting was redundant, it was best to
    > leave it alone.
    > He also seemed to say the network bandwidth was constant, and system
    > load rose with an 64bit system. This right? If he was using GENERIC on
    > a smp system he was only using 1 cpu with out a recompile. There is
    > just so much that could be wrong and he gives no information on his
    > system or settings.
    > Doess he have 2 amd64 pcs with 2 different installs of 5.3, or a
    > single machine that he ran both versions on? The router, is that a
    > third machine that was an amd64 system, or something else? He says
    > i386, but an up to date 5.3 world doesn't support 386 with out a work
    > around. The least commom setting is now 486, but a build for 686 would
    > be better. Did he tell you if he had polling on?
    >
    > So I guess it is a good thing you were able to help him, because I
    > couldn't. Not to mention the flame bait you through out, well, that
    > would be wrong. _______________________________________________
    >
    > --------- Previous Message
    >
    > No, thats not what I was talking about. They were tuning the MAX_INTS
    > parameter for the em
    > driver, which can hold off interrupts to reduce system overhead.
    > Instead of minimizing the load,
    > they were focused on squeezing a few extra bits out of iperf, which is
    > not how you tune
    > performance. If you get 700Kb/s and have a 95% load and can get
    > 695Kb/s with 60% load,
    > which is better? Plus they were testing with a regular PCI bus, so
    > they were hitting the
    > wall on the bus throughput, which changes all the timings, so it was
    > just a stupid test in
    > general.

    I would say 60% load. Now I completely understand what you were saying.

    >
    > I'm not 100% sure of what he was saying, but I've seen the same thing.
    > I take an i386 disk
    > and pop on an amd64 disk with the same settings, except for the 3 or 4
    > required differences,
    > and the i386 machine has WAY less network load. So maybe your
    > buildworld runs faster,
    > but the whole interrupt/process switching mechanism runs like crap, so
    > you likely have a
    > slower machine. I haven't seen any test that shows otherwise, just a
    > bunch of swell
    > guys swearing that one thing is faster than another.
    >
    > I understand that you don't want to hear the truth, so flame away. But
    > its not going to make
    > things any better.

    Ahh! More flame bait! I just didn't like you platitudinal and
    unproductive message that I believe would just drive Boris onto linux
    and leave a possible open problem on FreeBSD for some one else to
    discover latter. It's not that I don't want to hear the truth, you were
    just not saying anything worth his time. But atleast now we can get
    some where to help him and the amd64 port. I also had the idea that
    Boris was just trolling because he has not responded, just said FreeBSD
    was bad and left us to duke it out.

    > _______________________________________________
    > freebsd-questions@freebsd.org mailing list
    > http://lists.freebsd.org/mailman/listinfo/freebsd-questions
    > To unsubscribe, send any mail to
    > "freebsd-questions-unsubscribe@freebsd.org"
    >
    So the whole interrupt/process switching mechanism runs like crap with
    the amd64 build? Since I don't have a amd64 system, and you might hav
    access to atleast 1, how about getting a little info on the irqs? Look
    at systat -vmstat or vmstat -i under load? aybe report it back? I
    wonder if the irq rates are changing, or irqs are taking longer to
    service. Either there is a problem. Ofcourse some hardware info would
    be nice, chipset and cpu? Maybe you script vmstat -i for a log, and use
    netperf too?

    I like Nick's followup. I would guese Boris may have a problem with
    proper hardware support. I can't really said it is bad hardware if
    speeds are the same, just high load(right?). Maybe the driver he is
    using is not good for 64bit as it is for 32bit?

    I think if Boris studies the thread I like to below he will be alright.

    Check this out:
    http://www.atm.tut.fi/list-archive/freebsd-stable/thrd66.html
    http://docs.freebsd.org/cgi/mid.cgi?200502171636.10361.drice

    Inparticular:
    http://www.atm.tut.fi/list-archive/freebsd-stable/msg19651.html
    http://www.atm.tut.fi/list-archive/freebsd-stable/msg19679.html
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