Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation

From	Wanpeng Li <kernellwp@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation
Date	2016-04-24 01:00 +0200
Message-ID	<rreGS-2oB-1@gated-at.bofh.it> (permalink)
References	(1 earlier) <rq52V-3Hq-7@gated-at.bofh.it> <rql7I-8rt-27@gated-at.bofh.it> <rqoIi-2PN-3@gated-at.bofh.it> <rqyoh-23w-1@gated-at.bofh.it> <rqJ0n-2pv-21@gated-at.bofh.it>
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2016-04-22 21:07 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
> 2016-04-22 09:40+0800, Wanpeng Li:
>> 2016-04-21 23:29 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
>>> x86 vcpu_id encodes APIC ID and APIC ID encodes CPU topology by
>>> reserving blocks of bits for socket/core/thread, so if core or thread
>>> count isn't a power of two, then the set of valid APIC IDs is sparse,
>>
>>              ^^^^^^^^^^^^^^^^^^^
>>              ^^^^^^^
>> Is this the root reason why recommand max vCPUs per vm is 160 and the
>> KVM_MAX_VCPUS is 255 instead of due to perforamnce concern?
>
> No, the recommended amout of VCPUs is 160 because I didn't bump it after
> PLE stopped killing big guests. :/
>
> You can get full 255 VCPU guest with a proper configuration, e.g.
> "-smp 255" or "-smp 255,cores=8" and the only problem is scalability,
> but I don't know of anything that doesn't scale to that point.
>
> (Scaling up to 2^32 is harder, because you don't want O(N) search, nor
>  full allocation on smaller guests.  Neither is a big problem now.)

I see, thanks Radim.

Regards,
Wanpeng Li

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[PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-20 17:50 +0200
  Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation James Hogan <james.hogan@imgtec.com> - 2016-04-20 18:20 +0200
  Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Cornelia Huck <cornelia.huck@de.ibm.com> - 2016-04-20 18:50 +0200
    Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation David Hildenbrand <dahi@linux.vnet.ibm.com> - 2016-04-21 15:40 +0200
  Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation James Hogan <james.hogan@imgtec.com> - 2016-04-20 19:10 +0200
    Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-20 19:30 +0200
      Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-20 20:00 +0200
        Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-20 20:40 +0200
  Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-20 19:10 +0200
  Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-20 20:30 +0200
    Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-21 13:40 +0200
      Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Cornelia Huck <cornelia.huck@de.ibm.com> - 2016-04-21 14:30 +0200
        Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-21 15:10 +0200
      Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation David Hildenbrand <dahi@linux.vnet.ibm.com> - 2016-04-21 15:30 +0200
      Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-21 17:30 +0200
        Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-21 18:00 +0200
          Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-21 18:10 +0200
            Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-21 19:20 +0200
              Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-21 19:40 +0200
                Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Greg Kurz <gkurz@linux.vnet.ibm.com> - 2016-04-21 20:10 +0200
        Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Wanpeng Li <kernellwp@gmail.com> - 2016-04-22 03:50 +0200
          Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Radim Krčmář <rkrcmar@redhat.com> - 2016-04-22 15:10 +0200
            Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Wanpeng Li <kernellwp@gmail.com> - 2016-04-24 01:00 +0200

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