Re: [RFC] X86 SMP cpu enumeration changes

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As a followup to the message I posted earlier, I found that the following patch restores the old behavior of allowing maxcpus to effectively turn off hyperthreading. In case you missed my earlier message, in 2.6.16 through at least 2.6.19 using the maxcpus trick will fail to use all of your physical cpus.

Although this patch works for me, I am quite sure that this patch is unacceptable to folks using CPU hotplug, however. One alternative would be to make the two lines of code in each location conditional on CONFIG_HOTPLUG_CPU and !CONFIG_HOTPLUG_CPU respectively, but that seems a little ugly.

Does anyone have a better fix?

I know my mailer smashes the patch, but this is intended for discussion rather than application.

--- a/arch/i386/kernel/mpparse.c 2006-11-29 15:57:37.000000000 -0600
+++ b/arch/i386/kernel/mpparse.c	2007-06-06 16:41:06.635814335 -0500
@@ -180,9 +180,6 @@ static void __devinit MP_processor_info
        }
        apic_version[m->mpc_apicid] = ver;
-       phys_cpu = apicid_to_cpu_present(apicid);
- physids_or(phys_cpu_present_map, phys_cpu_present_map, phys_cpu);
-
        if (num_processors >= NR_CPUS) {
printk(KERN_WARNING "WARNING: NR_CPUS limit of %i reached."
                        "  Processor ignored.\n", NR_CPUS);
@@ -195,6 +192,9 @@ static void __devinit MP_processor_info
                return;
        }
+       phys_cpu = apicid_to_cpu_present(apicid);
+ physids_or(phys_cpu_present_map, phys_cpu_present_map, phys_cpu);
+
        cpu_set(num_processors, cpu_possible_map);
        num_processors++;


--
Mark Rustad, [email protected]


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