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Re: [Xen-devel] IA32 vcpu-pin broken?

To: "Apparao, Padmashree K" <padmashree.k.apparao@xxxxxxxxx>
Subject: Re: [Xen-devel] IA32 vcpu-pin broken?
From: Emmanuel Ackaouy <ack@xxxxxxxxxxxxx>
Date: Mon, 18 Sep 2006 17:56:46 +0100
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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;

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

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