RE: [Xen-users] amd64 system only seeing 3.5gb instead of 4gb of memory

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: James Harper [mailto:james.harper@xxxxxxxxxxxxxxxx] 
> Sent: 15 June 2007 11:16
> To: Petersson, Mats; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-users] amd64 system only seeing 3.5gb 
> instead of 4gb of memory
> 
> > 
> > Further to what has already been said (all of which is sensible and
> good
> > suggestions):
> > 1. Assuming you have an AMD processor, you need a procesor 
> that is Rev
> E
> > or later.
> 
> First half of cat /proc/cpuinfo:
> 
> processor       : 0
> vendor_id       : AuthenticAMD
> cpu family      : 15
> model           : 67
> model name      : Dual-Core AMD Opteron(tm) Processor 1210
> stepping        : 3
> cpu MHz         : 1800.018
> cache size      : 1024 KB
> physical id     : 0
> siblings        : 1
> core id         : 0
> cpu cores       : 1
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 1
> wp              : yes
> flags           : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36
> clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext
> 3dnow pni cx16 lahf_lm cmp_legacy svm cr8_legacy
> bogomips        : 4501.72
> TLB size        : 1024 4K pages
> clflush size    : 64
> cache_alignment : 64
> address sizes   : 40 bits physical, 48 bits virtual
> power management: ts fid vid ttp tm stc
> 
> 40 bits of physical addressing should be enough shouldn't it? 
> Or are you
> talking about revision E being required for the remapping?

Yes, (flexible) memory hoisting is only available on Rev E or later. Not
an issue as your machine is a Rev F processor (Opteron 1xxx, 2xxx and
8xxx are Rev F). 
> 
> > 2. You need to have PAE or 64-bit mode to see any memory 
> ABOVE 4GB (so
> > even if it's remapped, non-PAE will not be able to "get 
> there" because
> > it's strictly limited to 32-bit memory addresses, which is 4GB in
> total
> > - this is why the PCI memory is located around the end of 4GB).
> 
> xm info:
> 
> host                   : dev
> release                : 2.6.18-4-xen-amd64
> version                : #1 SMP Fri May 4 02:40:51 UTC 2007
> machine                : x86_64
> nr_cpus                : 2
> 
> definitely running in 64 bit mode yes?

Looks so. 
> 
> > 3. Your BIOS must enable "memory hoisting", which is the techie name
> for
> > "move memory from under PCI space to someplace else".
> 
> Now this I haven't checked... I'll have a look this weekend.
> 
> Subsequent reading showed at least one other person had such 
> a problem,
> and it was probably related to grub passing a 'basic' memory 
> map instead
> of the modern type (I even followed up to that post 
> originally... what a
> short memory I have these days!!!). I can probably confirm 
> this from xm
> dmesg:
> 
> (XEN) Command line: /xen-3.1.0-1-amd64.gz
> (XEN)  0000000000000000 - 000000000009f000 (usable)
> (XEN)  0000000000100000 - 00000000dfff0000 (usable)
> (XEN) System RAM: 3583MB (3669564kB)
> (XEN) Xen heap: 13MB (14176kB)
> (XEN) Domain heap initialised: DMA width 32 bits

So that tells us that Xen is doing exactly what the BIOS/Grub says - and
of course, GRUB does things differently for Xen and a normal Linux
distro, simply because it's using a different model of booting. 

--
Mats
> 
> D'oh!
> 
> I'll try and get into the office this weekend and have a better look.
> There are no BIOS upgrades at this point.
> 
> Thanks
> 
> James
> 
> 
> 



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