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Re: [Xen-devel] [PATCH] Only include online cpus in cpu_mask_to_apicid_f

To: "Sheng Yang" <sheng.yang@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Only include online cpus in cpu_mask_to_apicid_flat
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Wed, 01 Sep 2010 10:14:52 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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>>> On 01.09.10 at 05:39, "Yang, Sheng" <sheng.yang@xxxxxxxxx> wrote:
> Yes, here is the patch with modification of other variants.

If indeed an adjustment like this is needed, then this (and other similar

>@@ -71,6 +72,11 @@
> unsigned int cpu_mask_to_apicid_phys(cpumask_t cpumask)
> {
>+      int cpu;
>       /* As we are using single CPU as destination, pick only one CPU here */
>-      return cpu_physical_id(first_cpu(cpumask));
>+      for_each_cpu_mask(cpu, cpumask) {
>+              if (cpu_online(cpu))
>+                      break;
>+      }
>+      return cpu_physical_id(cpu);
> }

is both insufficient: You need to handle the case where you don't
find any online CPU in the mask (at least by adding a respective

But I tend to agree with Keir that this shouldn't be done here -
these functions are simple accessors, which shouldn't enforce
any policy. Higher level code, if it doesn't already, should be
adjusted to never allow offline CPUs to slip through.


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