Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755247AbaGWC3u (ORCPT ); Tue, 22 Jul 2014 22:29:50 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:35098 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754537AbaGWC3c (ORCPT ); Tue, 22 Jul 2014 22:29:32 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.0.1 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20120718-3 Message-ID: <53CF1DE3.7090001@jp.fujitsu.com> Date: Wed, 23 Jul 2014 11:28:51 +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: Toshi Kani CC: , , , , , , , , , , , , , Subject: Re: [PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU References: <53C77C2B.1030000@jp.fujitsu.com> <1406053776.15077.13.camel@misato.fc.hp.com> In-Reply-To: <1406053776.15077.13.camel@misato.fc.hp.com> 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 (2014/07/23 3:29), Toshi Kani wrote: > 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 >> Suggested-by: Borislav Petkov > >> --- >> 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. I'll update it soon. > > Otherwise, the change looks good. > > Reviewed-by: Toshi Kani Thank you for review. Thanks, Yasuaki Ishimatsu > > 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/