x86: "nosmp" command line option should force the system into UP mode (5f2eb550) · Commits · 戴 / test

Bits set in cpu_possible_mask prior to the execution of prefill_possible_map() (i.e. when parsing ACPI or MPS tables) would prevent the SMP alternatives logic from switching to UP mode, plus unnecessary setup of per-CPU data for CPUs that can never come online. Additionally, without CONFIG_HOTPLUG_CPU disabled CPUs can never come online, and hence setting cpu_possible_mask bits for them is again a simple waste of resources. Signed-off-by:

Jan Beulich <jbeulich@novell.com> LKML-Reference: <201005241913.o4OJDH3Z010874@imap1.linux-foundation.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

H. Peter Anvin <hpa@linux.intel.com>

arch/x86/kernel/smpboot.c

+23 −3

Original line number	Diff line number	Diff line
		@@ -1215,9 +1215,17 @@ __init void prefill_possible_map(void)
		if (!num_processors)
		num_processors = 1;

		if (setup_possible_cpus == -1)
		possible = num_processors + disabled_cpus;
		else
		i = setup_max_cpus ?: 1;
		if (setup_possible_cpus == -1) {
		possible = num_processors;
		#ifdef CONFIG_HOTPLUG_CPU
		if (setup_max_cpus)
		possible += disabled_cpus;
		#else
		if (possible > i)
		possible = i;
		#endif
		} else
		possible = setup_possible_cpus;

		total_cpus = max_t(int, possible, num_processors + disabled_cpus);
		@@ -1230,11 +1238,23 @@ __init void prefill_possible_map(void)
		possible = nr_cpu_ids;
		}

		#ifdef CONFIG_HOTPLUG_CPU
		if (!setup_max_cpus)
		#endif
		if (possible > i) {
		printk(KERN_WARNING
		"%d Processors exceeds max_cpus limit of %u\n",
		possible, setup_max_cpus);
		possible = i;
		}

		printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
		possible, max_t(int, possible - num_processors, 0));

		for (i = 0; i < possible; i++)
		set_cpu_possible(i, true);
		for (; i < NR_CPUS; i++)
		set_cpu_possible(i, false);

		nr_cpu_ids = possible;
		}

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