Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751365AbaG1EUB (ORCPT ); Mon, 28 Jul 2014 00:20:01 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:49559 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750781AbaG1EUA (ORCPT ); Mon, 28 Jul 2014 00:20:00 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.0.1 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20120718-3 Message-ID: <53D5CF2A.2030007@jp.fujitsu.com> Date: Mon, 28 Jul 2014 13:18:50 +0900 From: Yasuaki Ishimatsu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: , , , , , , CC: , , , , , , , Subject: Re: [PATCH v4] x86,cpu-hotplug: assign same CPU number to readded CPU References: <53CF2A81.7080505@jp.fujitsu.com> In-Reply-To: <53CF2A81.7080505@jp.fujitsu.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-SecurityPolicyCheck-GC: OK by FENCE-Mail X-TM-AS-MML: No Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > Suggested-by: Borislav Petkov > Reviewed-by: Toshi Kani > --- > 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 majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/