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Message-ID: <1406053776.15077.13.camel@misato.fc.hp.com> Date: Tue, 22 Jul 2014 12:29:36 -0600 From: Toshi Kani <toshi.kani@...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, 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, umgwanakikbuti@...il.com, peterz@...radead.org Subject: Re: [PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU On Thu, 2014-07-17 at 16:32 +0900, 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> > --- > v2: change cpuid to cpunum > v3: fix Borislav's email address of Suggested-by > fix typo (ACPI ID to APIC ID) > --- > 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..5dc3e50 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_used_bits, CONFIG_NR_CPUS); > +static struct cpumask *const cpu_used_mask = to_cpumask(cpu_used_bits); I think the name of cpu_used_mask is confusing since the term "used" sounds some state of CPU, which is not the case here. How about cpu_number_mask? This is more specific and avoids such confusion. Otherwise, the change looks good. Reviewed-by: Toshi Kani <toshi.kani@...com> Thanks, -Toshi > + > +/* > * Get the LAPIC version > */ ^^ ps. I had a problem in applying this patch since there was an extra blank character at the begging of unchanged lines. But this might be an issue in my mailer. -- 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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