Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping.

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Hi tj,

On 09/11/2015 03:55 AM, Tejun Heo wrote:
Hello,

So, overall, I think this is the right way to go although I have no
idea whether the acpi part is okay.

Thank you very much for reviewing. :)


+/*
+ * Current allocated max logical CPU ID plus 1.
+ * All allocated CPU ID should be in [0, max_logical_cpuid),
+ * so the maximum of max_logical_cpuid is nr_cpu_ids.
+ *
+ * NOTE: Reserve 0 for BSP.
+ */
+static int max_logical_cpuid = 1;
Rename it to nr_logical_cpuids and just mention that it's allocated
contiguously?

OK.


+static int cpuid_to_apicid[] = {
+	[0 ... NR_CPUS - 1] = -1,
+};
And maybe mention how the two variables are synchronized?

User should call allocate_logical_cpuid() to get a new logical cpuid.
This allocator will ensure the synchronization.

Will mention it in the comment.


+static int allocate_logical_cpuid(int apicid)
+{
+	int i;
+
+	/*
+	 * cpuid <-> apicid mapping is persistent, so when a cpu is up,
+	 * check if the kernel has allocated a cpuid for it.
+	 */
+	for (i = 0; i < max_logical_cpuid; i++) {
+		if (cpuid_to_apicid[i] == apicid)
+			return i;
+	}
+
+	/* Allocate a new cpuid. */
+	if (max_logical_cpuid >= nr_cpu_ids) {
+		WARN_ONCE(1, "Only %d processors supported."
+			     "Processor %d/0x%x and the rest are ignored.\n",
+			     nr_cpu_ids - 1, max_logical_cpuid, apicid);
+		return -1;
+	}
So, the original code didn't have this failure mode, why is this
different for the new code?

It is not different. Since max_logical_cpuid is new, this is ensure it won't
go beyond NR_CPUS.

Thanks.


Thanks.


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