Hi ,
I just saw this from xen wiki-faq.
4.3. When I boot vmlinuz-xen0, why doesn''t it detect my second CPU?
You may expect the initial Linux instance to detect all your CPUs, but
this is never the case. Your secondary CPUs will have been detected by
Xen, but we do not currently support multi-CPU virtual machines, so
vmlinuz-xen0 can only see one CPU. Of course, you can create extra VMs
and run them on your other CPUs. Support for multi-processor VMs is in
the pipeline.
does that mean xen doesn''t support 2 cpus??
man..
thanks in advance!
xin
_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users
Hi, That info is out of date, Xen ha supported SMP guests throughout the 3.x series, so it should work fine for you. It''s normal to run dom0 as a UP guest though, since this is often only used for IO. Dedicating a core or hyperthread to it can improve performance. Cheers, Mark On Tuesday 13 March 2007 00:44, Xin Chen wrote:> Hi , > > I just saw this from xen wiki-faq. > > > 4.3. When I boot vmlinuz-xen0, why doesn''t it detect my second CPU? > > You may expect the initial Linux instance to detect all your CPUs, but > this is never the case. Your secondary CPUs will have been detected by > Xen, but we do not currently support multi-CPU virtual machines, so > vmlinuz-xen0 can only see one CPU. Of course, you can create extra VMs > and run them on your other CPUs. Support for multi-processor VMs is in > the pipeline. > > > does that mean xen doesn''t support 2 cpus?? > > man.. > > thanks in advance! > xin > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users-- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Monday 12 March 2007, Mark Williamson wrote:> Hi, > > That info is out of date, Xen ha supported SMP guests throughout the 3.x > series, so it should work fine for you.not only that; but AFAICR, Xen 2.x did support multiple CPUs. the quoted text only explained that each domain (either DomU or Dom0) would get one ''virtual'' CPU each. -- Javier _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi Mark, thanks for your quick reply!!! by the way, It''s normal to run dom0 as a UP guest though what is UP guest ? how to do that?? sorry about my stupid.. thanks:) xin Mark Williamson wrote:>Hi, > >That info is out of date, Xen ha supported SMP guests throughout the 3.x >series, so it should work fine for you. > >It''s normal to run dom0 as a UP guest though, since this is often only used >for IO. Dedicating a core or hyperthread to it can improve performance. > >Cheers, >Mark > >On Tuesday 13 March 2007 00:44, Xin Chen wrote: > > >>Hi , >> >>I just saw this from xen wiki-faq. >> >> >> 4.3. When I boot vmlinuz-xen0, why doesn''t it detect my second CPU? >> >>You may expect the initial Linux instance to detect all your CPUs, but >>this is never the case. Your secondary CPUs will have been detected by >>Xen, but we do not currently support multi-CPU virtual machines, so >>vmlinuz-xen0 can only see one CPU. Of course, you can create extra VMs >>and run them on your other CPUs. Support for multi-processor VMs is in >>the pipeline. >> >> >>does that mean xen doesn''t support 2 cpus?? >> >>man.. >> >>thanks in advance! >>xin >> >>_______________________________________________ >>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
hmm, I see, it means no matter how many cpus you have, domain 0 will identify all the cpus as 1 super & virtual cpu. right? thanks! xin Javier Guerra wrote:>On Monday 12 March 2007, Mark Williamson wrote: > > >>Hi, >> >>That info is out of date, Xen ha supported SMP guests throughout the 3.x >>series, so it should work fine for you. >> >> > >not only that; but AFAICR, Xen 2.x did support multiple CPUs. the quoted text >only explained that each domain (either DomU or Dom0) would get one ''virtual'' >CPU each. > > > > >------------------------------------------------------------------------ > >_______________________________________________ >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 3/12/07, Xin Chen <xcheney@allette.com.au> wrote:> what is UP guest ? how to do that??Uni-processor. "vcpu=1" in the guest''s xen config - it''s also the default, which I noticed by looking through the xmexample1 example file... jerry -- "Oh joy! Rapture! I''ve got a brain" -Scarecrow _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On 3/12/07, Xin Chen <xcheney@allette.com.au> wrote:> hmm, I see, it means no matter how many cpus you have, domain 0 will > identify all the cpus as 1 super & virtual cpu. > right?Umm... No. Wrong. There are many possibilities for cpu assignment within dom0, and therefore, within domU''s. p.s. I yanked that entry out of the faq to reduce future confusion... jerry -- "Oh joy! Rapture! I''ve got a brain" -Scarecrow _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
cool. thanks for that!! :-) Jerry Amundson wrote:> On 3/12/07, Xin Chen <xcheney@allette.com.au> wrote: > >> what is UP guest ? how to do that?? > > > Uni-processor. "vcpu=1" in the guest''s xen config - it''s also the > default, which I noticed by looking through the xmexample1 example > file... > > jerry >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
OK! I see now. For guest system, they only know virtual cpu which domain 0 made.Domain0 is incharge of real cpus. Great. Thanks! ps: I did check the entry. It is gone! I don''t know you are the master! cool! xin Jerry Amundson wrote:> On 3/12/07, Xin Chen <xcheney@allette.com.au> wrote: > >> hmm, I see, it means no matter how many cpus you have, domain 0 will >> identify all the cpus as 1 super & virtual cpu. >> right? > > > Umm... No. Wrong. > There are many possibilities for cpu assignment within dom0, and > therefore, within domU''s. > > p.s. I yanked that entry out of the faq to reduce future confusion... > > jerry >_______________________________________________ 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 Xin Chen > Sent: 13 March 2007 01:55 > To: xen-users@lists.xensource.com > Subject: Re: [Xen-users] Xen Not Support multi-cpu?? > > OK! I see now. For guest system, they only know virtual cpu > which domain > 0 made.Domain0 is incharge of real cpus. > Great. Thanks!To be VERY PEDANTIC: VCPU''s are what ALL domains "know". The REAL CPU''s are handled by the hypervisor only. Whilst it''s true that Dom0 gives the instructions about how many real and virtual CPU''s a guest should use, it still is the hypervisor that enforces, controls and guarantees this. Dom0 in the sense of the Hypervisor is another guest - it just so happens that it''s got the "privileged flag" set. Think of Dom0 as a "root" user in Unix, and DomU as a "regular user", and you get the idea. -- Mats _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > That info is out of date, Xen ha supported SMP guests throughout the 3.x > > series, so it should work fine for you. > > not only that; but AFAICR, Xen 2.x did support multiple CPUs. the quoted > text only explained that each domain (either DomU or Dom0) would get one > ''virtual'' CPU each.Yep. Xen 1.x also supported SMP hosts, but also had the restriction that guests be UP. Cheers, Mark -- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Cool! Thanks u guys:) cheers! xin Petersson, Mats wrote:> > > > >>-----Original Message----- >>From: xen-users-bounces@lists.xensource.com >>[mailto:xen-users-bounces@lists.xensource.com] On Behalf Of Xin Chen >>Sent: 13 March 2007 01:55 >>To: xen-users@lists.xensource.com >>Subject: Re: [Xen-users] Xen Not Support multi-cpu?? >> >>OK! I see now. For guest system, they only know virtual cpu >>which domain >>0 made.Domain0 is incharge of real cpus. >>Great. Thanks! >> >> > >To be VERY PEDANTIC: VCPU''s are what ALL domains "know". The REAL CPU''s >are handled by the hypervisor only. Whilst it''s true that Dom0 gives the >instructions about how many real and virtual CPU''s a guest should use, >it still is the hypervisor that enforces, controls and guarantees this. > >Dom0 in the sense of the Hypervisor is another guest - it just so >happens that it''s got the "privileged flag" set. Think of Dom0 as a >"root" user in Unix, and DomU as a "regular user", and you get the idea. > >-- >Mats > > > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > > >To be VERY PEDANTIC: VCPU''s are what ALL domains "know". The REAL CPU''s > >are handled by the hypervisor only. Whilst it''s true that Dom0 gives the > >instructions about how many real and virtual CPU''s a guest should use, > >it still is the hypervisor that enforces, controls and guarantees this. > > > >Dom0 in the sense of the Hypervisor is another guest - it just so > >happens that it''s got the "privileged flag" set. Think of Dom0 as a > >"root" user in Unix, and DomU as a "regular user", and you get the idea. > > > >I get the idea. But I have another question about this. Should we compile the dom0 and domU kernels with SMP support? I have bought a server with 2 5130 cpu''s (quad core), which make the total cpu count 8. How do I have to understand the arrangement of cpu''s? One cpu for the dom0 (which doesn''t need SMP compiled then?), and some domU''s with two or 3 vcpu''s (heavily loaded ones -> they need SMP then?) and some domU''s with only 1 vcpu. So is it correct to say that I need SMP only for the domU kernels? Peter _______________________________________________ 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 > Peter Fastré > Sent: 15 March 2007 11:05 > To: xen-users@lists.xensource.com > Subject: Re: [Xen-users] Xen Not Support multi-cpu?? > > > >To be VERY PEDANTIC: VCPU''s are what ALL domains > "know". The REAL CPU''s > >are handled by the hypervisor only. Whilst it''s true > that Dom0 gives the > >instructions about how many real and virtual CPU''s a > guest should use, > >it still is the hypervisor that enforces, controls and > guarantees this. > > > >Dom0 in the sense of the Hypervisor is another guest - > it just so > >happens that it''s got the "privileged flag" set. Think > of Dom0 as a > >"root" user in Unix, and DomU as a "regular user", and > you get the idea. > > > > > > I get the idea. But I have another question about this. > Should we compile the dom0 and domU kernels with SMP support? > I have bought a server with 2 5130 cpu''s (quad core), which > make the total cpu count 8. > How do I have to understand the arrangement of cpu''s? One cpu > for the dom0 (which doesn''t need SMP compiled then?), and > some domU''s with two or 3 vcpu''s (heavily loaded ones -> they > need SMP then?) and some domU''s with only 1 vcpu. > So is it correct to say that I need SMP only for the domU kernels?If you want to make your own life easy, just compile one kernel for Dom0 and DomU with SMP enabled (which is default). But if you want to eek out the last couple of percent performance out of the kernel (assuming your apps spend a fair bit in the kernel), you may want to get rid of SMP for kernels that you don''t run more than one VCPU on. Note that there should be little difference between running SMP kernel or non-SMP kernel on a single (V)CPU, as the locks and such will never be contended, nor will there be cache-flushes for the locks. But of course, there are extra instructions to achieve locks in SMP, which will take some extra time from the execution. [And some locks will still be needed, as you still have the possibility of multiple threads running on the same CPU interacting with each other]. Note that the number of VCPU''s in a 8 core system is not limited to 8. You can have 8 VCPU''s for every domain should you wish to (and have a hundred domains -> 800 VCPU''s). It''s just that they can''t all run at once, of course! -- Mats> > Peter > > > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > I get the idea. But I have another question about this. > > Should we compile the dom0 and domU kernels with SMP support? > > I have bought a server with 2 5130 cpu''s (quad core), which > > make the total cpu count 8. > > How do I have to understand the arrangement of cpu''s? One cpu > > for the dom0 (which doesn''t need SMP compiled then?), and > > some domU''s with two or 3 vcpu''s (heavily loaded ones -> they > > need SMP then?) and some domU''s with only 1 vcpu. > > So is it correct to say that I need SMP only for the domU kernels? > > If you want to make your own life easy, just compile one kernel for Dom0 > and DomU with SMP enabled (which is default). > > But if you want to eek out the last couple of percent performance out of > the kernel (assuming your apps spend a fair bit in the kernel), you may > want to get rid of SMP for kernels that you don''t run more than one VCPU > on. Note that there should be little difference between running SMP kernel > or non-SMP kernel on a single (V)CPU, as the locks and such will never be > contended, nor will there be cache-flushes for the locks. But of course, > there are extra instructions to achieve locks in SMP, which will take some > extra time from the execution. [And some locks will still be needed, as you > still have the possibility of multiple threads running on the same CPU > interacting with each other].Does dom0 have to be SMP capable? It used to be at one stage, but I might be massively out of date here. If the "SMP alternatives" mode is compiled in the kernel will automatically reoptimise itself (even at runtime, last time I saw the patch!) for the number of (V)CPUs it has. So the overhead of having SMP support compiled into a UP guest can actually be quite a bit lower than one would usually expect. This is still marked experimental, I think.> Note that the number of VCPU''s in a 8 core system is not limited to 8. You > can have 8 VCPU''s for every domain should you wish to (and have a hundred > domains -> 800 VCPU''s). It''s just that they can''t all run at once, of > course!You could even have more than that - number of VCPUs for a domU can exceed the number of host CPUs (although that''s obviously probably not going useful from a performance PoV! Might be good for testing ... something, though.). Cheers, Mark -- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users