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Date: Fri, 11 Jul 2014 12:59:20 +0200 From: Borislav Petkov <bp@...en8.de> To: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com> Cc: Igor Mammedov <imammedo@...hat.com>, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org, toshi.kani@...com, huawei.libin@...wei.com, paul.gortmaker@...driver.com, linux-kernel@...r.kernel.org, srivatsa.bhat@...ux.vnet.ibm.com, umgwanakikbuti@...il.com, peterz@...radead.org Subject: Re: [PATCH] x86,cpu-hotplug: assign same CPU number to readded CPU On Fri, Jul 11, 2014 at 09:48:27AM +0900, Yasuaki Ishimatsu wrote: > >>+static int get_cpuid(int apicid) Btw this "cpuid" is misleading. Call it "cpu_num" or so. > >>+{ > >>+ 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? > > To assing new CPU number, I prepared new cpu bitmask. > > The following two steps are necessary to assign CPU number to APIC ID. > 1. Check whether APIC ID has been assigned CPU number > 2. Assign new CPU number if ACPI ID has not been assigned CPU number (it > means apicid_to_cpuid[] returns -1) > > Step 1. is checked by apicid_to_cpuid[]. And step 2. assigns new CPU > number by using cpu_used_mask. > > To keep cpu number, cpumask must not be cleared by hot removing CPU. > If cpumask is cleared by hot removing CPU, the cpumask cannot be used > to keep CPU number. > > Currently, cpu_present_map is used to assign CPU number. But the cpumask > is cleared by hot removing CPU since the mask is prepared to remember > existed CPUs in the system. So the cpu_present_map must be cleared > at CPU hot remove. > > I confirmed whether present cpumasks (cpu_possible_map, cpu_online_map > et al) is usable or not for this purpose. But there is no cpumask that > can be used to keep CPU number. So I prepared new cpu bitmask. > > >How about just finding the first apicid_to_cpuid[apicid] < 0 > >and dropping not needed anymore bitmask. > > When apicid_to_cpuid[] return -1, kernel assigns new CPU number. For > this, the cpu_used_mask is necessary. And we can't have that - we cannot have cores which had number X get number Y after hotplug. Can you send a full dmesg after you've done a physical node hotplug on a machine? Privately is fine too. Boot with "ignore_loglevel log_buf_len=10M debug apic=debug show_lapic=all" please. Thanks. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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