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

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Message-ID: <23159a7e-463a-2a5b-5aaa-ef7f0eb43547@intel.com>
Date:   Fri, 11 Aug 2017 15:49:59 +0800
From:   Lan Tianyu <tianyu.lan@...el.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, rkrcmar@...hat.com
Cc:     pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM/x86: Increase max vcpu number to 352

Hi Konrad:
	Thanks for your review.

On 2017年08月11日 01:50, Konrad Rzeszutek Wilk wrote:
> On Thu, Aug 10, 2017 at 06:00:59PM +0800, Lan Tianyu wrote:
>> Intel Xeon phi chip will support 352 logical threads. For HPC usage
>> case, it will create a huge VM with vcpu number as same as host cpus. This
>> patch is to increase max vcpu number to 352.
> 
> Why not 1024 or 4096?

This is on demand. We can set a higher number since KVM already has
x2apic and vIOMMU interrupt remapping support.

> 
> Are there any issues with increasing the value from 288 to 352 right now?

No found.

> 
> Also perhaps this should be made in an Kconfig entry?

That will be anther option but I find different platforms will define
different MAX_VCPU. If we introduce a generic Kconfig entry, different
platforms should have different range.

Radim & Paolo, Could you give some input? In qemu thread, we will set
max vcpu to 8192 for x86 VM. In KVM, The length of vcpu pointer array in
struct kvm and dest_vcpu_bitmap in kvm_irq_delivery_to_apic() are
specified by KVM_MAX_VCPUS. Should we keep align with Qemu?

-- 
Best regards
Tianyu Lan