AMD64 much slower than i386 on FreeBSD 5.4-pre
jason henson
jason at ec.rr.com
Wed Mar 23 21:48:27 PST 2005
em1897 at 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.
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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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