Dirk H. Schulz
2005-Nov-07 07:24 UTC
Re: SMP does not work as expected - was: Re: [Xen-users] Checking for SMP usage in xen stable
Tom Brown schrieb:>this is just the normal P4/xeon hyperthreading isn''t it? I don''t know what >an IBM x335 is... so I''m just guessing that hyperthreading is available. > >Yes, this is a Xeon that can do hyperthreading - but does SMP in Xen also work on hyperthreaded single cpus? I thought that hyperthreading is different from SMP. If that works I can distribute CPU power in finer chunks on a dual processor hyperthreading machine. I will test that. Dirk>-Tom > >On Mon, 7 Nov 2005, Dirk H. Schulz wrote: > > > >>Hi folks, >> >>I looked somewhat deeper into the smp issue with Xen 2.0.7. I found that >>smp is used even on machines with only one processor. >> >>This is xm list on an IBM x335, a dual processor board with one processor: >> >> Name Id Mem(MB) CPU State Time(s) >>Console >> Domain-0 0 123 0 r---- >>59931.7 >> webdynown01 5 511 1 -b--- >>193.5 9605 >> webstatown01 1 255 0 -b--- >>202.9 9601 >> >>I have configured CPU usage in the domU''s config files. So two of one >>CPUs are used, it seems. >> >>This is xm list on a single processor machine: >> >> Name Id Mem(MB) CPU State >>Time(s) Console >> Domain-0 0 123 0 >>r---- 5567.2 >> sync01 2 95 0 >> -b--- 1.8 9602 >> >>So it seems that on dual processor boards smp is somehow simulated if >>there is just one processor present. >> >>Is this a bug, or does it make sense somehow? >> >>And now my original question comes up again: How can I - reliably - >>verify that my xen kernel is running smp code? >> >>Dirk >> >>_______________________________________________ >>Xen-users mailing list >>Xen-users@lists.xensource.com >>http://lists.xensource.com/xen-users >> >> >> > >---------------------------------------------------------------------- >tbrown@BareMetal.com | Courage is doing what you''re afraid to do. >http://BareMetal.com/ | There can be no courage unless you''re scared. > | - Eddie Rickenbacker > > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Tom Brown
2005-Nov-07 07:51 UTC
Re: SMP does not work as expected - was: Re: [Xen-users] Checking for SMP usage in xen stable
On Mon, 7 Nov 2005, Dirk H. Schulz wrote:> Tom Brown schrieb: > > >this is just the normal P4/xeon hyperthreading isn''t it? I don''t know what > >an IBM x335 is... so I''m just guessing that hyperthreading is available. > > > > > > Yes, this is a Xeon that can do hyperthreading - but does SMP in Xen > also work on hyperthreaded single cpus? I thought that hyperthreading is > different from SMP.it is different ... hyperthreading only "looks" like SMP. I am no expert on it, but ran across something recently that indicated it was something Intel introduced to reduce the effect of the deep pipeline in their processors. The idea is that the processor can be working on two "programs" at the same time, and if the data or instructions for one of the programs is not available, the other one might be ready and able to make productive use of the CPU core.> If that works I can distribute CPU power in finer chunks on a dual > processor hyperthreading machine.My understanding is that in the context of "task switching", it _is_ usefull, I would assume it is like having an extra set of registers. I believe the Xen docs suggest that you dedicate one thread of one CPU to dom0. -Tom ---------------------------------------------------------------------- tbrown@BareMetal.com | Courage is doing what you''re afraid to do. http://BareMetal.com/ | There can be no courage unless you''re scared. | - Eddie Rickenbacker _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users