Ping. (2014/07/23 12:22), Yasuaki Ishimatsu wrote:
llc_shared_map is not cleared even if CPU is offline or hot removed. So when hot-plugging CPU and assigning new CPU number to hot-added CPU, the mask has wrong value. The mask is used by CSF schduler to create sched_domain. So it breaks CFS scheduler.Here is a example on my system. My system has 4 sockets and each socket has 15 cores and HT is enabled. In this case, each core of sockes is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 Socket#2 | 30-44, 90-104 Socket#3 | 45-59, 105-119 Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000. It means that last level cache of Socket#2 is shared with CPU#30-44 and 90-104. When hot-removing socket#2 and #3, each core of sockets is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains having 0x3fff80000001fffc0000000. After that, when hot-adding socket#2 and #3, each core of sockets is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 Socket#2 | 30-59 Socket#3 | 90-119 Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000. It means that last level cache of Socket#2 is shared with CPU#30-59 and 90-104. So the mask has wrong value. At first, I cleared hot-removed CPU number's bit from llc_shared_map when hot removing CPU. But Borislav suggested that the problem will disappear if readded CPU is assigned same CPU number. And llc_shared_map must not be changed. So the patch assigns same CPU number to readded CPU by linking CPU number to APIC ID. And by the patch, the problem disappers. Signed-off-by: Yasuaki Ishimatsu <isimatu.yasu...@jp.fujitsu.com> Suggested-by: Borislav Petkov <b...@alien8.de> Reviewed-by: Toshi Kani <toshi.k...@hp.com> --- v2: change cpuid to cpunum v3: fix Borislav's email address of Suggested-by fix typo (ACPI ID to APIC ID) v4: change cpu_used_xxx to cpu_number_xxx --- arch/x86/kernel/apic/apic.c | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index ad28db7..5cecc3b 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -220,6 +220,23 @@ static void apic_pm_activate(void); static unsigned long apic_phys; /* + * Bind APIC ID to Logical CPU number + * Logical CPU number to APIC ID does not change by this array + * even if CPU is hotplugged. So don't clear the array even if + * CPU is hot-removed + */ +static int apicid_to_cpunum[MAX_LOCAL_APIC] = { + [0 ... MAX_LOCAL_APIC-1] = -1, +}; + +/* + * Represent Logical CPU number bound to APIC ID + * Don't clear a bit even if CPU is hot-removed + */ +static DECLARE_BITMAP(cpu_number_bits, CONFIG_NR_CPUS); +static struct cpumask *const cpu_number_mask = to_cpumask(cpu_number_bits); + +/* * Get the LAPIC version */ static inline int lapic_get_version(void) @@ -2122,6 +2139,17 @@ void disconnect_bsp_APIC(int virt_wire_setup) apic_write(APIC_LVT1, value); } +static int get_cpunum(int apicid) +{ + int cpu; + + cpu = apicid_to_cpunum[apicid]; + if (cpu < 0) + cpu = cpumask_next_zero(-1, cpu_number_mask); + + return cpu; +} + int generic_processor_info(int apicid, int version) { int cpu, max = nr_cpu_ids; @@ -2199,7 +2227,9 @@ int generic_processor_info(int apicid, int version) */ cpu = 0; } else - cpu = cpumask_next_zero(-1, cpu_present_mask); + cpu = get_cpunum(apicid); + + apicid_to_cpunum[apicid] = cpu; /* * Validate version @@ -2228,6 +2258,7 @@ int generic_processor_info(int apicid, int version) early_per_cpu(x86_cpu_to_logical_apicid, cpu) = apic->x86_32_early_logical_apicid(cpu); #endif + cpumask_set_cpu(cpu, cpu_number_mask); set_cpu_possible(cpu, true); set_cpu_present(cpu, true); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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