Re: [PATCH] x86,cpu-hotplug: assign same CPU number to readded CPU

[Yasuaki Ishimatsu]

Hi Borislav,

(2014/07/11 19:59), Borislav Petkov wrote:
> 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.

O.K.
I'll update it.

> > > > +{
> > > > +	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.

O.K.
I'll send dmesg.

Thanks,
Yasuaki Ishimatsu

> Boot with
>
> 	"ignore_loglevel log_buf_len=10M debug apic=debug show_lapic=all"
>
> please.
>
> Thanks.


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