Messages in this thread Patch in this message | | | Date | Fri, 19 Mar 2010 16:24:24 +0000 | From | "Jan Beulich" <> | Subject | [PATCH] x86: "nosmp" command line option should force the system into UP mode |
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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>
--- arch/x86/kernel/smpboot.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-)
--- linux-2.6.34-rc1/arch/x86/kernel/smpboot.c +++ 2.6.34-rc1-x86-nosmp-UP-mode/arch/x86/kernel/smpboot.c @@ -1214,9 +1214,17 @@ __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); @@ -1229,11 +1237,23 @@ __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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