> -----Original Message----- > From: kernelnewbies-bounces@xxxxxxxxxxxxxxxxx [mailto:kernelnewbies- > bounces@xxxxxxxxxxxxxxxxx] On Behalf Of Robert P. J. Day > Sent: Monday, October 22, 2012 12:47 PM > To: Kernel Newbies > Subject: online, possible and disabled cpus > > > at this point, i'm trying to rationalize why i'm seeing this in the > output of dmesg: > > [ 0.000000] smpboot: Allowing 16 CPUs, 8 hotplug CPUs > > on my quad-core asus laptop, as in -- where is that "16" coming from? > if i list /proc/cpuinfo, i see 8 processors, so i'm just trying to > understand what "16" represents, so let's read backwards. > > first, that line above seems to be printed from > arch/x86/kernel/smpboot.c: > > pr_info("Allowing %d CPUs, %d hotplug CPUs\n", > possible, max_t(int, possible - num_processors, 0)); > > so, *apparently*, by that time, the boot process has established that > there are 16 "possible" processors, but only 8 actual ones. but who > decided there were 16 "possible" processors? > > just above that in the same file, we have: > > 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); > > whoa, so it appears that we get "possible" cpus from adding the > number of *actual* cpus to the number of "disabled" cpus. but what is > a "disabled" cpu, and who decides how many there are? > > last thing i notice is this earlier in my dmesg output: > > [ 0.000000] ACPI: PM-Timer IO Port: 0x408 > [ 0.000000] ACPI: Local APIC address 0xfee00000 > [ 0.000000] ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x02] lapic_id[0x02] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x03] lapic_id[0x04] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x04] lapic_id[0x06] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x05] lapic_id[0x01] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x06] lapic_id[0x03] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x07] lapic_id[0x05] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x08] lapic_id[0x07] enabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x09] lapic_id[0x08] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x0a] lapic_id[0x09] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x0b] lapic_id[0x0a] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x0c] lapic_id[0x0b] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x0d] lapic_id[0x0c] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x0e] lapic_id[0x0d] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x0f] lapic_id[0x0e] disabled) > [ 0.000000] ACPI: LAPIC (acpi_id[0x10] lapic_id[0x0f] disabled) > > which certainly seems to be related to all of this -- 8 enabled and 8 > disabled. so i'm going to keep following this back, unless someone > wants to break it to me what is going on. > You'll have to investigate those disabled CPUs, but I'm guessing that the presence or absence of hyperthreading may have something to do with it. Craig Jackson _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
