Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754651AbaGQAIo (ORCPT ); Wed, 16 Jul 2014 20:08:44 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:36028 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752818AbaGQAIm (ORCPT ); Wed, 16 Jul 2014 20:08:42 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.0.1 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20120718-3 Message-ID: <53C713D2.7000106@jp.fujitsu.com> Date: Thu, 17 Jul 2014 09:07:46 +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: Borislav Petkov , Tony Luck CC: , , , , , , , , , , , Subject: Re: [PATCH v2] x86,cpu-hotplug: assign same CPU number to readded CPU References: <53C62AAF.7060509@jp.fujitsu.com> <20140716111107.GB17464@pd.tnic> In-Reply-To: <20140716111107.GB17464@pd.tnic> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-SecurityPolicyCheck-GC: OK by FENCE-Mail Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2014/07/16 20:11), Borislav Petkov wrote: > On Wed, Jul 16, 2014 at 04:33:03PM +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 > > You can remove the "1" above as the domain is .de :-) Sorry for my mistake. I'll update soon. > > Ok, so after looking at the dmesg you sent me, it looks like it works as > expected. > > Apparently, the cores get enumerated in the order they're listed in SRAT > - this also explains the mapping between APIC ID and core number in > Linux. > > Your patch looks simple enough as you're basically making that mapping > explicit with apicid_to_cpunum and make sure it remains stable when the > cores reappear. > > And since APIC ID doesn't change across physical hotplug (does it?), it > all works as expected. > > But, since this is BIOS and BIOS does crazy hacks to accomodate b0rked > OSes, I'd like it if Tony looked at this too, whether it makes sense and > whether that solution is fine. > > @Tony: the text should explain it all, leaving in the rest. Thank you for reviewing my patch and confirming dmesg. I wait Tony's comment. Thanks, Yasuaki Ishimatsu > > Thanks. > >> --- >> v2: change cpuid to cpunum >> --- >> 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 ACPI 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); >> + >> +/* >> * 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_used_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_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/