From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bandan Das Subject: Re: KVM_MAX_VCPU hard limit of 255 on x86 Date: Fri, 01 Apr 2016 17:55:07 -0400 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain Cc: kvm@vger.kernel.org To: Hardik H Bagdi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42069 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752688AbcDAVzK (ORCPT ); Fri, 1 Apr 2016 17:55:10 -0400 Cc: Radim =?utf-8?B?S3LEjW3DocWZ?= In-Reply-To: (Hardik H. Bagdi's message of "Fri, 1 Apr 2016 17:19:47 -0400") Sender: kvm-owner@vger.kernel.org List-ID: Hardik H Bagdi writes: > Hello, > > For research, I am experimenting with increasing the number of VCPUs > in the guest OS. > I can increase the number of VCPUs till 255 in the guest OS but more > than that results in the following error- > > kvm_init_vcpu failed: Invalid argument > > The hardcodede value of 255 can be found here for x86. > ./arch/x86/include/asm/kvm_host.h:38:#define KVM_MAX_VCPUS 255 > > #define a new value is not successful i.e. the same error persists. > I'm using qemu 2.5.0 with host kernel 3.19.0 > Any help will be really appreciated. Radim (Cced) might have more info but the short answer is that you can't just simply increase the number. For >255, you need x2apic with interrupt remapping which is still missing. > Thank you, > Hardik Bagdi > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html