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Bug 105349 - With an SMP kernel NUMA should be enabled for increased memory performance
With an SMP kernel NUMA should be enabled for increased memory performance
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: kernel (Show other bugs)
All Linux
medium Severity medium
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Assigned To: Arjan van de Ven
David Lawrence
Depends On:
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Reported: 2003-09-25 05:40 EDT by Albert Fluegel
Modified: 2007-11-30 17:06 EST (History)
0 users

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Last Closed: 2003-09-26 04:09:40 EDT
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Description Albert Fluegel 2003-09-25 05:40:03 EDT
Description of problem:
Not a problem, but a feature request.
Some guy from IBM stated, that with NUMA enabled on
an Opteron SMP system memory performance is sped up
by up to 30%. Please set
in /usr/src/redhat/SOURCES/kernel-2.4.21-x86_64-smp.config

Version-Release number of selected component (if applicable):

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Comment 1 Albert Fluegel 2003-09-25 11:17:41 EDT
the kernel cannot be built with NUMA support turned on.
Reason is a loop in #includes. First, the asm/mmzone.h
needs a definition from linux/mmzone.h . Including
linuz/mmzone.h before asm/mmzone.h leads to an error
because some wait_q_type is not defined. Reason is, that
mmzone.h and wait.h include each other.
Comment 2 Arjan van de Ven 2003-09-26 03:03:06 EDT
I wonder what the IBM person bases this on, especially since
1) Opteron systems hardly are NUMA
2) The kernel by default (including ours) does not have a lot of NUMA support
   (some other linux distros patch in a lot of this, which slows down the normal
case. gaining 30% relative to that is easier of course :)
Comment 3 Albert Fluegel 2003-09-26 03:41:57 EDT
AFAIK Opteron SMP systems are NUMA by design. Each part of the memory is
assigned to a CPU. When a CPU wants to access memory, that is assigned
to the other CPU, the access passes the memory controller of the other
CPU, what makes the access slower than a local one.
I really would like to benchmark this, but as explained i don't get
the kernel built due to type definition problems :-(
Comment 4 Arjan van de Ven 2003-09-26 03:45:21 EDT
They are NUMA, however the NUMA factor is very very close to 1 (unlike some
other boxes where the NUMA speed is in the order of 15); academic research has
shown that a numa factor of 2 is about the turnover point for the OS doing
special NUMA hacks. A performance improvement of 30% is certainly believable for
systems with a large NUMA factor (like the IBM x440) but I have a hard time
believing it for real world use on AMD Opteron machines.

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