Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752765AbaGJJ1V (ORCPT ); Thu, 10 Jul 2014 05:27:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6886 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751746AbaGJJ1T (ORCPT ); Thu, 10 Jul 2014 05:27:19 -0400 Date: Thu, 10 Jul 2014 11:26:09 +0200 From: Igor Mammedov To: Yasuaki Ishimatsu Cc: , , , , , , , , , , , Subject: Re: [PATCH] x86,cpu-hotplug: assign same CPU number to readded CPU Message-ID: <20140710112609.0b0eb294@nial.usersys.redhat.com> In-Reply-To: <53BE51CE.40208@jp.fujitsu.com> References: <53BE51CE.40208@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 10 Jul 2014 17:41:50 +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 > Suggested-by: Borislav Petkov > --- > arch/x86/kernel/apic/apic.c | 32 +++++++++++++++++++++++++++++++- > 1 file changed, 31 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c > index ad28db7..1cc715b 100644 > --- a/arch/x86/kernel/apic/apic.c > +++ b/arch/x86/kernel/apic/apic.c > @@ -220,6 +220,22 @@ static void apic_pm_activate(void); > static unsigned long apic_phys; > > /* > + * Bind ACPI ID to CPU ID > + * CPU ID 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_cpuid[MAX_LOCAL_APIC] = { > + [0 ... MAX_LOCAL_APIC-1] = -1, > +}; > + > +/* > + * Represent CPU ID bound to APIC > + * 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); > + > +/* > * Get the LAPIC version > */ > static inline int lapic_get_version(void) > @@ -2122,6 +2138,17 @@ void disconnect_bsp_APIC(int virt_wire_setup) > apic_write(APIC_LVT1, value); > } > > +static int get_cpuid(int apicid) > +{ > + int cpuid; > + > + cpuid = apicid_to_cpuid[apicid]; > + if (cpuid < 0) > + cpuid = cpumask_next_zero(-1, cpu_used_mask); Why do you need additional cpu bitmask? How about just finding the first apicid_to_cpuid[apicid] < 0 and dropping not needed anymore bitmask. > + > + return cpuid; > +} > + > int generic_processor_info(int apicid, int version) > { > int cpu, max = nr_cpu_ids; > @@ -2199,7 +2226,9 @@ int generic_processor_info(int apicid, int version) > */ > cpu = 0; > } else > - cpu = cpumask_next_zero(-1, cpu_present_mask); > + cpu = get_cpuid(apicid); > + > + apicid_to_cpuid[apicid] = cpu; > > /* > * Validate version > @@ -2228,6 +2257,7 @@ 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_used_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/