linux-kernel - Re: Opteron box and 4Gb memory

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Message-ID: <20071105001847.546565c4@werewolf>
Date:	Mon, 5 Nov 2007 00:18:47 +0100
From:	"J.A. Magallón" <jamagallon@....com>
To:	"Linux-Kernel, " <linux-kernel@...r.kernel.org>
Subject: Re: Opteron box and 4Gb memory

On Thu, 25 Oct 2007 14:58:10 -0700, "H. Peter Anvin" <hpa@...or.com> wrote:

> J.A. Magallon wrote:
> > Hi...
> > 
> > I have some Quad-Opteron boxes with 4Gb memory and two of them are
> > running two different Linux distros.
> > 
> > Box one sees 4Gb of memory, but box two just sees 3.
> > Their mtrr setups are different:
> > 
> > Why ? Is it a bios setup problem ? A kernel problem ?
> > grep HIGHMEN in configs for both kernels does not give anything, so
> > I still understand less this thing...
> > 
> 
> It would depend on how the BIOS programmed the memory controllers.  For 
> 32-bit (and lots of device) compatibility, a memory hole is required 
> below 4 GB.  Not all memory controllers can remap memory in the 3-4 GB 
> range above the 4 GB memory; I'm not sure if that varies with the 
> different Opteron processors.
> 

Well, I was able to get about 3 Gb with MTRR=discrete in the BIOS,
but I'm still in the process to find the 'software hole' option to get
the rest of the 4Gb...

But now another (perhaps related) question has arised...
I like all those 5-line progams to test system performance...;).
I just wrote a simple program that sums/muls int/float vectors with
scalar/sse operations. And my opteron box looks terribly slow.

This is my MacPro, Xeon 5130:

belly:~/bn> bn  
	proc: 4 x MacPro1,1 @ 2000 MHz
	ram:  2048 Mb
	os:   unx, Darwin, 9.0.0
	cc:   gcc-4.0.1
vector size   : 8 x 1024 x 1024
allocation:     0.01 ms
int scl add: ..........   36.78 ms,  228.07 Mips   |  114.03 Mips  /GHz
int scl mul: ..........   34.30 ms,  244.60 Mips   |  122.30 Mips  /GHz
flt scl add: ..........   34.28 ms,  244.73 Mflops |  122.37 Mflops/GHz
flt vec add: ..........    7.89 ms, 1063.15 Mflops |  531.58 Mflops/GHz
flt scl mul: ..........   34.20 ms,  245.28 Mflops |  122.64 Mflops/GHz
flt vec mul: ..........    7.90 ms, 1061.77 Mflops |  530.89 Mflops/GHz
total:       3322.19 ms

This is a normal (I think) opteron box (Opteron 846):

selene:~/bn> g  
	proc: 4 x x86_64 @ 2004 MHz
	ram:  3496 Mb
	os:   unx, Linux, 2.6.9-42.0.10.ELsmp
	cc:   gcc-4.0.2
vector size   : 8 x 1024 x 1024
allocation:     0.05 ms
int scl add: ..........   45.98 ms,  182.42 Mips   |   91.03 Mips  /GHz
int scl mul: ..........   44.31 ms,  189.30 Mips   |   94.46 Mips  /GHz
flt scl add: ..........   44.52 ms,  188.41 Mflops |   94.02 Mflops/GHz
flt vec add: ..........   10.03 ms,  836.70 Mflops |  417.52 Mflops/GHz
flt scl mul: ..........   43.32 ms,  193.63 Mflops |   96.62 Mflops/GHz
flt vec mul: ..........   10.02 ms,  836.98 Mflops |  417.65 Mflops/GHz
total:       4705.07 ms

And this is my opteron (Opteron 275)

cicely:~/bn> g  
	proc: 4 x x86_64 @ 2200 MHz
	ram:  2914 Mb
	os:   unx, Linux, 2.6.23.1-desktop-1mdv
	cc:   gcc-4.0.2
vector size   : 8 x 1024 x 1024
allocation:     0.03 ms
int scl add: ..........   87.67 ms,   95.68 Mips   |   43.49 Mips  /GHz
int scl mul: ..........   85.48 ms,   98.13 Mips   |   44.61 Mips  /GHz
flt scl add: ..........   85.90 ms,   97.66 Mflops |   44.39 Mflops/GHz
flt vec add: ..........   19.51 ms,  429.96 Mflops |  195.44 Mflops/GHz
flt scl mul: ..........   85.86 ms,   97.70 Mflops |   44.41 Mflops/GHz
flt vec mul: ..........   19.50 ms,  430.11 Mflops |  195.50 Mflops/GHz
total:       6334.96 ms

As I read in AMD site, the only difference that matters in models is
the xx5 vx xx6, related to fequency, but the processors should be just
the same.

As this only does intensive memory/fp operations, I'm not going to blame
gcc nor kernel versions here (I have compared gcc 3.4, 4.0, 4.1, and 4.2
on one of the boxes and results are very similar, the code is really
stupid and not very suitable for compiler smartness...).
I suspect it is a memory problem. It can be hardware or caused by
incorrect BIOS/kernel-mtrr setup:

selene:~> cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size=16384MB: write-back, count=1
reg01: base=0xf0000000 (3840MB), size= 256MB: uncachable, count=1

cicely:~> cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size= 512MB: write-back, count=1
reg02: base=0xa0000000 (2560MB), size= 256MB: write-back, count=1
reg03: base=0xb0000000 (2816MB), size= 128MB: write-back, count=1
reg04: base=0xb8000000 (2944MB), size=  16MB: write-back, count=1


Any idea on what can be going on here ? I have asked the 'good opteron'
admin info about the mobo an memory of the box.

Any help will be _very_ appreciated.

TIA

--
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2008.1 (Cooker) for i586
Linux 2.6.23-jam01 (gcc 4.2.2 20070909 (4.2.2-0.RC.1mdv2008.0)) SMP PREEMPT
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
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