Re: [Xen-devel] How to get the cache miss ratio of Guest VM

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Am Mittwoch 11 Januar 2012, 12:07:48 schrieb George Dunlap:
> 2012/1/10 gavin <gbtux@xxxxxxx>:
> > I noticed that the credit2 scheduling algorithm has one runqueue every L2
> > cache that is shared by cores in one socket. If vCPUs, which need to
> > communicate more with each other, are assigned to the cores sharing the same
> > L2 cache, the L2 cache miss ratio of Guest VM may be reduced. And also, the
> > performance of the Guest VM will be improved. Is it right? But, how to test
> > the cache miss ratio of L2 in Guest VM? Are the tools that used to test the
> > cache miss ratio in non-virtualized environment can be used in Xen Guest VM?
> 
> Looking through the code, it looks like performance counters are
> passed-through to HVM guests, both on AMD and Intel.  And it appears
> that Fujitsu is regularly using the performance counters on Intel at
> least (since Deitmar Hahn has been the one posting patches for new
> performance counters).
> 
> It appears that there is no support for access to performance counters
> in PV mode, other than to use them for xenoprofile (which will not
> allow you to read the counters directly).
> 
> So it's worth trying whatever method you normally use to look at
> performance counters while running in an HVM guest.

Yes, only HVM guests. On Intel (for what I sent patches) only some processors
are supported.
You have to add the hypervisor boot variable 'vpmu' in your grub/menu.lst or
whatever.
If your processor is not supported you will see a message in the hypervisor
boot logging (it's printed from the sorce xen/arch/x86/hvm/vpmu.c function
vpmu_initialise()). 

Dietmar.

>  -George

-- 
Company details: http://ts.fujitsu.com/imprint.html

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