Re: [Xen-devel] CAP and performance problem

[Massimo Canonico <mex@xxxxxxxxxxxx>]

On 06/06/2013 04:12 PM, Dario Faggioli wrote:
> On gio, 2013-06-06 at 15:55 +0200, Massimo Canonico wrote:
> > On 06/06/2013 03:02 PM, Juergen Gross wrote:
> > > You added the boot parameter for the hypervisor, not dom0?
> > Fedora, after few seconds, asks you which kernel do you want to use. You
> > can add some parameter in the command line who launches the kernel. So,
> > I add "cpufreq=none" in the command line.
> IIRC, that won't do, as you're most likely modifying Dom0 command line,
> you need to be sure you're adding that bit to the Xen boot command
> line.
>
> I think you can do that dynamically, by editing the grub2 parameters
> on-line, as you're saying you did, but you have to make sure you affect
> Xen and not Linux. IIRC
>
> Otherwise, you should go to /etc/default/grub (I think), look for
> something like GRUB_CMDLINE_XEN (I think) add the "cpufreq=none" string
> there and regenerate grub.cfg by running:
>
> # grub2-mkconfig -o /boot/grub2/grub.cfg
>
> After that, I recommend double checking that /boot/grub2/grub.cfg has
> it, and has it in the right place.
>
> Feel free to post it here, if you're not sure about that...
>
> > > Could you try:
> > >
> > > xl vcpu-list; sleep 10; xl vcpu-list
> > >
> > > when the test is running and post the output?
> > >
> > >
> > > Juergen
> > here we go:
> >
> > [root@csitest ~]# xl vcpu-list; sleep 10; xl vcpu-list
> > Name                                ID  VCPU   CPU State   Time(s) CPU
> > Affinity
> > Domain-0                             0     0    0   ---      23.0  0
> > Domain-0                             0     1    0   ---      10.5  0
> > Domain-0                             0     2    0   ---       8.5  0
> > Domain-0                             0     3    0   r--       6.8  0
> > rubis-web                            1     0    2   r--    2968.5  2
> > Name                                ID  VCPU   CPU State   Time(s) CPU
> > Affinity
> > Domain-0                             0     0    0   ---      23.0  0
> > Domain-0                             0     1    0   r--      10.6  0
> > Domain-0                             0     2    0   ---       8.5  0
> > Domain-0                             0     3    0   ---       6.8  0
> > rubis-web                            1     0    2   r--    2973.5  2
> So, rubis-web's vcpu ran for 5 secs, which sounds right. I see why
> Jurgen asked you to do that, but not how he plans to squeeze anything
> more than that from these numbers... Waiting for him to enlighten us
> again! ;-P
>
> > Concerning the George's question:
> > > Have you checked your BIOS for performance settings?
> > I'm not sure what you mean for "BIOS perfomance settings". To my best
> > knowledge, in the BIOS I have to be sure that the "hw virtualization" is
> > enabled.
> I think he was referring to something related to poerformance vs. power
> management, i.e., cpufreq/speedstep tweaks, and stuff like that, if ou
> have any in the BIOS... Do you?
>
> Regards,
> Dario
Actually it seems that the problem is related to a BIOS setting. In my 
HP server, there were a parameter called "HP power regulator" that I set 
to "HP Static High-performance power" (before it was set to "dynamic 
performance power") and now I get what it is expected: cap 50% make my 
application twice longer than when cap is 100%.
Thanks to all of you guys. I think that this should be reported in the 
doc where the cap mechanism is explained.
Cheer,
 Massimo

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