Re: [Xen-devel] ATI/AMD VGA passthru report

[<djmagee@xxxxxxxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxx] On Behalf Of Pavel Mateja
> Sent: Wednesday, May 09, 2012 2:59 PM
> To: xen-devel@xxxxxxxxxxxxx
> Cc: Konrad Rzeszutek Wilk
> Subject: Re: [Xen-devel] ATI/AMD VGA passthru report
> 
> On Wed 9. of May 2012 19:44:26 Konrad Rzeszutek Wilk wrote:
> > > I tried to run some games as well but the feeling is much worse
> > > compared to older configuration. Like lags..
> >
> > Do the lags disappear if you pin the vCPUs?
> 
> One stupid question:
> I tried:
> xl vcpu-list
> Name                                ID  VCPU   CPU State   Time(s) CPU
> Affinity
> Domain-0                             0     0    3   -b-      74.8  any
> cpu
> Domain-0                             0     1    2   -b-       7.7  any
> cpu
> Domain-0                             0     2    5   -b-       7.4  any
> cpu
> Domain-0                             0     3    2   -b-       8.2  any
> cpu
> Domain-0                             0     4    0   r--       8.4  any
> cpu
> Domain-0                             0     5    1   -b-       7.4  any
> cpu
> windows                              2     0    3   -b-      27.8  1-5
> windows                              2     1    4   -b-      23.5  1-5
> windows                              2     2    5   -b-      24.9  1-5
> windows                              2     3    1   -b-      27.3  1-5
> windows                              2     4    1   -b-      25.2  1-5
> 
> Do the last two lines mean that two vCPUs in winows are running on one
> real?
> The output changes and mostly is real - virtual cpu mapped one to one.
> I have to study the pinning more. I guess I was wrong when I wrote I
> already have it.

In my experience passing through video and sound devices, performance in the 
guest is noticeably better if you pin the domU vCpus 1:1 with pCpus.  As an 
example, on a 4 core machine, I'll pin the dom0 cpus 1:1 using the 
dom0_vcpu_pin boot line argument, and restrict dom0 to 1 or 2 cpus.  Then, for 
a 2 vcpu domu, after I start the guest, I'll do 'xl vcpu-pin 1 0 2; xl vcpu-pin 
1 1 3'.  This way guest cpu 0 is always running on physical cpu 2 and guest 1 
on physical 3.

I don't think there's currently a way in xl config to do this on xl create, 
which is why I pin after I create the domain.  That is, I think you can only 
set the affinity for all vcpus in the config file, and not per-vcpu.

> --
> Pavel Mateja
> 
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