Xen devel - Sep 2006 - IA32 vcpu-pin broken?

Hi,

 

I want dom0 and a guest to be on the same physical cpu. I have booted
dom0 with 1 cpu and also modified /etc/xen/xend-config.sxp to say
"dom0-cpus 1".


I cannot pin the dom0 cpu however, I can pin the guest cpu to be the
same as dom0 pcpu. However, the moment I start running an app in the
guest, dom0 pcpu changes to something else.

 

I know it used to work before. I am using the xen-unstable from Aug
29th. (there is a patch for IA64 on dom0 pinning, but nothing for IA32)

 

Before xm vcpu-list

Name                              ID  VCPU  CPU  State
Time(s)              CPU Affinity

Domain-0                           0     0    1                   r--
2254.4              any cpu

Domain-0                           0     1    -                 --p
0.0                   any cpu

Domain-0                           0     2    -                 --p
0.0                    any cpu

Domain-0                           0     3    -                 --p
0.0                    any cpu

Guest1                                2    0    1                  -b-
2244.2             2

 

After xm vcpu-list

Name                              ID  VCPU  CPU  State
Time(s)              CPU Affinity

Domain-0                           0     0      3                r--
2254.4              any cpu

Domain-0                           0     1    -                 --p
0.0                   any cpu

Domain-0                           0     2    -                 --p
0.0                   any cpu

Domain-0                           0     3    -                 --p
0.0                   any cpu

Guest1                                2    0      1                -b-
2244.2             2

 

 

Thanks

Padma



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On Mon, Sep 18, 2006 at 09:36:57AM -0700, Apparao, Padmashree K
wrote:
>    I want dom0 and a guest to be on the same physical cpu. I have booted
dom0
>    with 1 cpu and also modified /etc/xen/xend-config.sxp to say
"dom0-cpus
>    1".
> 
>    I cannot pin the dom0 cpu however, I can pin the guest cpu to be the
same
>    as dom0 pcpu. However, the moment I start running an app in the guest,
>    dom0 pcpu changes to something else.
> 
>    I know it used to work before. I am using the xen-unstable from Aug
29^th.
>    (there is a patch for IA64 on dom0 pinning, but nothing for IA32)
It looks like the code in xen/common/domctl.c for
XEN_DOMCTL_getvcpuaffinity now rejects all operations
on the current VCPU (DOM0 VCPU0 on a UP dom0). Before,
it used to leave this up to the per-scheduler implementation
of set_affinity. The credit scheduler implementation allows
a new mask which contained the current cpu in it in this case.

See snipped from xen/common/domctl.c:

        [...]
        if ( op->cmd == XEN_DOMCTL_setvcpuaffinity )
        {
            if ( v == current )
            {
                ret = -EINVAL;
                put_domain(d);
                break;
            }
        [...]

So assuming the right checks still exist in the per-scheduler
implementations of set_affinity, we could remove this check.

Argueably though, we should just extend the IA64 patch to x86.
It should be trivial to do so. The changeset in question is
11453:019b7c756ddb.

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