My processor is AMD Athlon(tm) 64 X2 Dual Core Processor 5200+ and I''ve got 6 Gb of memory. I''m planning to put up a few database / web servers under RHEL5. Should I install 32bit or 64bit OS for my dom0 / domUs? I remember faintly reading from somewhere that you benefit from 64bit only if you have lots of memory (over 8 gigs). Is this true? Regards, Peter _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
PAE (which all modern x86 cpus have) will support up to 64GB physical. Main restriction is that for an application to support more than 4GB of addressable memory on 32 bit PAE systems, they have to be compiled a special way. If you don''t have any processes which want to address more than 4GB, 32 bit PAE will work fine for you. I don''t think 64bit xen is considered fully baked yet, although it certainly is workable for investigation purposes (from experience). Joe.> -----Original Message----- > From: xen-users-bounces@lists.xensource.com [mailto:xen-users- > bounces@lists.xensource.com] On Behalf Of Peter Peltonen > Sent: Thursday, March 01, 2007 2:25 PM > To: xen-users@lists.xensource.com > Subject: [Xen-users] 32bit or 64bit? > > My processor is AMD Athlon(tm) 64 X2 Dual Core Processor 5200+ and > I''ve got 6 Gb of memory. > > I''m planning to put up a few database / web servers under RHEL5. > > Should I install 32bit or 64bit OS for my dom0 / domUs? > > I remember faintly reading from somewhere that you benefit from 64bit > only if you have > lots of memory (over 8 gigs). Is this true? > > Regards, > Peter > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Thu, 1 Mar 2007, Kraska, Joe A (US SSA) wrote:> I don''t think 64bit xen is considered fully baked yet, although it > certainly is workable for investigation purposes (from experience).Can you point us at more detail about problems in 64-bit that are not in 32-bit? I''ve heard a few other people say similar things, but I have a couple emt64 boxes running in 64-bit mode just fine right now, and I''m thinking about putting up another shortly. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Thu, 2007-03-01 at 17:19 -0800, Luke S. Crawford wrote:> On Thu, 1 Mar 2007, Kraska, Joe A (US SSA) wrote: > > I don''t think 64bit xen is considered fully baked yet, although it > > certainly is workable for investigation purposes (from experience). > > Can you point us at more detail about problems in 64-bit that are not in > 32-bit? I''ve heard a few other people say similar things, but I have a > couple emt64 boxes running in 64-bit mode just fine right now, and I''m > thinking about putting up another shortly.One of the major ones had nothing to do with Xen, or CPU architecture. People installed 64 bit xen hypervisor + kernel then used 32 bit guest templates and were rather confused as to why it didn''t work. Other people confuse some of what was getting notorious in UML on a 64 bit kernel (in particular regarding nesting, I believe) and concluded the issue must also apply to Xen. And then there was the one about when you walk under a ladder or break a mirror, your kernel starts selling drugs and ends up in juvi hall. There were a few obvious install oopses with 3.0.2 64 on some GNU distros, but this had more to do with python-64 than it did Xen or its patched Kernel. I think the python-twisted meta packages weren''t suggesting everything they needed or something. Only a few times, did I ever help someone work on an obvious "mysterious" problem that only went away using a 32 bit hypervisor and kernel, and I''m not so sure that wasn''t just attributable to cheap hardware. If you have a tried in true 32 bit xen0 / xenU and 64 bit xen0 / xenU of like versions there''s no reason they can''t co-exist (that I found). I tend to run all 32 or all 64, however,and by habit and preference usually lean to 32 bit. If it works, go with the flow. Best, --Tim> _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On 2 Mar 2007 at 0:24, Peter Peltonen wrote:> My processor is AMD Athlon(tm) 64 X2 Dual Core Processor 5200+ and > I''ve got 6 Gb of memory. > > I''m planning to put up a few database / web servers under RHEL5. > > Should I install 32bit or 64bit OS for my dom0 / domUs? > > I remember faintly reading from somewhere that you benefit from 64bit > only if you have > lots of memory (over 8 gigs). Is this true?I''d say > 2 GB, and I''d say if you are dealing with large files like DVD images, a true 64 bit register can handle the amount of data (=file size) more easily. Regards, Ulrich _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On 1 Mar 2007 at 15:11, Kraska, Joe A (US SSA) wrote:> > PAE (which all modern x86 cpus have) will support up to 64GB physical. > > Main restriction is that for an application to support more than 4GB > of addressable memory on 32 bit PAE systems, they have to be compiled > a special way. If you don''t have any processes which want to address > more than 4GB, 32 bit PAE will work fine for you.Unaddressable physical memory is quite uninteresting: You can''t mem-map a DVD image in 32bit mode, PAE or not.> > I don''t think 64bit xen is considered fully baked yet, although it > certainly is workable for investigation purposes (from experience).I run SLES10 x86_64 with less trouble than those trying to mess with PAE on this list it seems. Regards, Ulrich _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> -----Original Message----- > From: xen-users-bounces@lists.xensource.com > [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of > Ulrich Windl > Sent: 02 March 2007 08:27 > To: xen-users@lists.xensource.com > Subject: RE: [Xen-users] 32bit or 64bit? > > On 1 Mar 2007 at 15:11, Kraska, Joe A (US SSA) wrote: > > > > > PAE (which all modern x86 cpus have) will support up to > 64GB physical.In Xen, some of the memory address bits are used for other purposes, which limits Xen''s usable memory in PAE to 16GB [I''m not sure EXACTLY what causes this restriction, but I''m 99.999% sure that this is the limit for 32-bit PAE].> > > > Main restriction is that for an application to support more than 4GB > > of addressable memory on 32 bit PAE systems, they have to > be compiled > > a special way. If you don''t have any processes which want to address > > more than 4GB, 32 bit PAE will work fine for you. > > Unaddressable physical memory is quite uninteresting: You > can''t mem-map a DVD > image in 32bit mode, PAE or not.Yes, and as far as I know, there''s no way around the 32-bit barrier - and even this is more like a 2-3GB barrier, as some memory space HAS to be mapped to the kernel-space so that interrupts and system calls will work. A 32-bit APPLICATION in 64-bit kernel only looses about 1% of the memory space to Kernel space (for the shim-layer to translate from 32 to 64 bit data structures), which means that a single application can without problems use 3.95GB of memory, even if the app is 32-bit. In 64-bit, each application can address more memory than any 8-socket AMD64 machine can harbour (each socket allows up to 8 sticks of memory -> 64 sticks, 64 x 4GB per sticks -> 256GB).> > > > > I don''t think 64bit xen is considered fully baked yet, although it > > certainly is workable for investigation purposes (from experience). > > I run SLES10 x86_64 with less trouble than those trying to > mess with PAE on this > list it seems.I''ve been using 64-bit Xen for the last 12 months or more, and whilst running xen-unstable is always a bit of a challenge, I''d say most of the bugs that I see are not 64-bit only - the code to deal with 64-bit only is only a little bit (startup-code, page-table handling and instruction decoding are the parts that are different - and that''s a few thousand lines in a project that is roughly 100k lines - and bugs are generally relatively evenly distributed in the code, so percentage-wise the 64-bit only bugs should be only a few). There are some problems running 64-bit HVM guests that have to do with handling of 64-bit instructions and simply that 64-bit guests do things different than 32-bit guests, but those are being ironed out as soon as we can root-cause them (the hard part is to figure out which code-sequence causes the problem, and what''s wrong with the code, which is particularly hard when the actual problem happens thousands of instructions later, in a piece of code that we may not have source-code for!) -- Mats> > Regards, > Ulrich > > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users > > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> Can you point us at more detail about problems in 64-bit that are notin> 32-bit? I''ve heard a few other people say similar things, but I havea> couple emt64 boxes running in 64-bit mode just fine right now, and I''m > thinking about putting up another shortly.All my Xen installs are 64 bit. Representatives of the Xen Source corporations, the authors of Xen, have said that "64 bit isn''t fully baked yet," and won''t be out for another 3 months or so. That''s why it''s not in the commercial product yet. I''ve certainly had bugs in my xen installations. Whether or not these are due to 64 bit, I have no idea. I merely take it as gospel that when the authors say something isn''t ready, they probably know something that I don''t. :) Joe. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Kraska, Joe A (US SSA) wrote:>> Can you point us at more detail about problems in 64-bit that are not >> > in > >> 32-bit? I''ve heard a few other people say similar things, but I have >> > a > >> couple emt64 boxes running in 64-bit mode just fine right now, and I''m >> thinking about putting up another shortly. >> > > Representatives of the Xen Source corporations, > the authors of Xen, have said that "64 bit isn''t fully baked yet," and > won''t be out for another 3 months or so. That''s why it''s not in the commercial > product yet.Maybe its the other way around? :-) -- Per Andreas Buer / Linpro AS t: 21 54 41 21 / m: 958 39 117 http://linpro.no/ - Ledende på Linux og åpen kildekode. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users