Re: [PATCH] KVM/x86: Increase max vcpu number to 352

From	Radim Krčmář <rkrcmar@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] KVM/x86: Increase max vcpu number to 352
Date	2017-08-15 16:30 +0200
Message-ID	<ueL10-2pR-7@gated-at.bofh.it> (permalink)
References	(2 earlier) <udd1n-LV-1@gated-at.bofh.it> <uddkJ-17M-1@gated-at.bofh.it> <udhRp-3Vr-47@gated-at.bofh.it> <udnWO-7ym-29@gated-at.bofh.it> <ueAoX-4hM-37@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

2017-08-15 11:00+0800, Lan Tianyu:
> On 2017年08月12日 03:35, Konrad Rzeszutek Wilk wrote:
>> On Fri, Aug 11, 2017 at 03:00:20PM +0200, Radim Krčmář wrote:
>>> 2017-08-11 10:11+0200, David Hildenbrand:
>>>> On 11.08.2017 09:49, Lan Tianyu wrote:
>>>>> On 2017年08月11日 01:50, Konrad Rzeszutek Wilk wrote:
>>>>>> Are there any issues with increasing the value from 288 to 352 right now?
>>>>>
>>>>> No found.
>>>
>>> Yeah, the only issue until around 2^20 (when we reach the maximum of
>>> logical x2APIC addressing) should be the size of per-VM arrays when only
>>> few VCPUs are going to be used.

(I was talking only about the KVM side.)

>> Migration with 352 CPUs all being busy dirtying memory and also poking
>> at various I/O ports (say all of them dirtying the VGA) is no problem?
> 
> This depends on what kind of workload is running during migration. I
> think this may affect service down time since there maybe a lot of dirty
> memory data to transfer after stopping vcpus. This also depends on how
> user sets "migrate_set_downtime" for qemu. But I think increasing vcpus
> will break migration function.

Utilizing post-copy in the last migration phase should make migration of
busy big guests possible.  (I agree that pre-copy in not going to be
feasible.)

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Lan Tianyu <tianyu.lan@intel.com> - 2017-08-15 05:10 +0200
  Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-08-15 16:20 +0200
    Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Radim Krčmář <rkrcmar@redhat.com> - 2017-08-15 18:20 +0200
      Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-08-18 16:00 +0200
        Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Radim Krčmář <rkrcmar@redhat.com> - 2017-08-21 17:50 +0200
    Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Lan Tianyu <tianyu.lan@intel.com> - 2017-08-16 05:20 +0200
      Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-08-18 16:30 +0200
  Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Radim Krčmář <rkrcmar@redhat.com> - 2017-08-15 16:30 +0200

csiph-web