From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Fri, 22 Apr 2016 15:07:20 +0200 (CEST) Received: from mx1.redhat.com ([209.132.183.28]:50244 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27026472AbcDVNHSx1Gl3 (ORCPT ); Fri, 22 Apr 2016 15:07:18 +0200 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D8813C05E16B; Fri, 22 Apr 2016 13:07:10 +0000 (UTC) Received: from potion (dhcp-1-215.brq.redhat.com [10.34.1.215]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id u3MD76cp021970; Fri, 22 Apr 2016 09:07:07 -0400 Received: by potion (sSMTP sendmail emulation); Fri, 22 Apr 2016 15:07:06 +0200 Date: Fri, 22 Apr 2016 15:07:06 +0200 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Wanpeng Li Cc: Greg Kurz , Paolo Bonzini , james.hogan@imgtec.com, Ingo Molnar , linux-mips@linux-mips.org, kvm , "linux-kernel@vger.kernel.org" , qemu-ppc@nongnu.org, Cornelia Huck , Paul Mackerras , David Gibson Subject: Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation Message-ID: <20160422130705.GD7202@potion> References: <146116689259.20666.15860134511726195550.stgit@bahia.huguette.org> <20160420182909.GB4044@potion> <20160421132958.0e9292d5@bahia.huguette.org> <20160421152916.GA30356@potion> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 53201 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: rkrcmar@redhat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips 2016-04-22 09:40+0800, Wanpeng Li: > 2016-04-21 23:29 GMT+08:00 Radim Krčmář : >> 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.)