Messages in this thread | | | Date | Wed, 23 Jul 2014 11:28:51 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU |
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(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 <isimatu.yasuaki@jp.fujitsu.com> >> Suggested-by: Borislav Petkov <bp@alien8.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.
I'll update it soon.
> > Otherwise, the change looks good. > > Reviewed-by: Toshi Kani <toshi.kani@hp.com>
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. > >
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