SMP performance on drgonfly
kris at obsecurity.org
Sun May 20 12:10:49 PDT 2007
On 2007-05-19, Erik Wikström <erik-wikstrom at telia.com> wrote:
> On 2007-05-19 01:58, Kris Kennaway wrote:
>> On Fri, May 18, 2007 at 04:46:27PM -0700, Matthew Dillon wrote:
>>> A large chunk of the kernel still runs under the big giant
>>> lock, including the light weight processes that libthread_xu
>>> uses, so something like mysql is going to hit a lot of BGL
>> Oh, OK.
>> What subsystems are out from under the big giant lock, so I can look
>> for another benchmark to compare with? Also, what profiling and
>> contention measurement tools do you have, so I can try to confirm that
>> this is the issue?
>>> You may be able to get DragonFly to run on the machines you
>>> were having problems with by compiling it with SMP but
>>> without APIC_IO. With that combination DragonFly will use
>>> the PIC in SMP mode, which usually works.
>> The issue is that I cannot even install with a UP kernel, so I can't
>> recompile to test this. I posted with more details about this problem
>> a few months ago.
> You should be able to build a new install CD, with the needed kernel
> options, on the computer where you got it running. Check out the
> nrelease framework for more details.
I dont think it is likely that Matt's suggestion will work given that
UP kernels do not boot, indicating it's not an SMP APIC issue. Also
now that I have this other machine running I don't currently have a
motivation to try on 8-core AMD machines.
I was hoping that Matt would reply to my questions above so I could
try to find a more level playing field on which to compare Dragonfly
and FreeBSD, but I'm afraid that the answer is that there currently
are *no* kernel subsystems that are not Giant-locked, so all workloads
will perform poorly on DragonFly (and there are no specialized tools
for studying SMP behaviour -- certainly I couldn't find any when I
Can someone confirm whether this is true?
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