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Date: Mon, 15 Sep 2014 06:25:59 +0200 From: Mike Galbraith <umgwanakikbuti@...il.com> To: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com> Cc: tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, bp@...en8.de, gong.chen@...ux.intel.com, tony.luck@...el.com, toshi.kani@...com, x86@...nel.org, imammedo@...hat.com, huawei.libin@...wei.com, paul.gortmaker@...driver.com, linux-kernel@...r.kernel.org, srivatsa.bhat@...ux.vnet.ibm.com, peterz@...radead.org, Wanpeng Li <wanpeng.li@...ux.intel.com>, Linn Crosetto <linn@...com> Subject: Re: [PATCH v5] x86,cpu-hotplug: assign same CPU number to readded CPU On Thu, 2014-09-11 at 16:21 +0900, Yasuaki Ishimatsu wrote: > There is no response for two months since posting v4. > What can I do for pushing the patch to upstream? Looks to me like we have two patches floating about for more or less the same problem, this one, and... https://lkml.org/lkml/2014/7/29/159 ..this one, which you reviewed, and HP both reviewed and tested. We seem to kinda stuck with Boris having said don't diddle the cpu_llc_shared_map, but HP/Intel saying that this map diddling fixes their explosions. If your alternative is preferred over diddling cpu_llc_shared_map, perhaps HP/Intel can test/confirm that their explosions stay gone? > Thanks, > Yasuaki Ishimatsu > > (2014/09/04 11:46), 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.yasuaki@...fujitsu.com> > > Suggested-by: Borislav Petkov <bp@...en8.de> > > Reviewed-by: Toshi Kani <toshi.kani@...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 > > v5: rebase to 3.17-rc3 > > --- > > 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 6776027..c476827 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) > > @@ -2109,6 +2126,17 @@ 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; > > @@ -2186,7 +2214,9 @@ 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 > > @@ -2215,6 +2245,7 @@ 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 majordomo@...r.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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