Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752328AbdHOOUh (ORCPT ); Tue, 15 Aug 2017 10:20:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52294 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751882AbdHOOUf (ORCPT ); Tue, 15 Aug 2017 10:20:35 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com B48F62D0FC6 Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=rkrcmar@redhat.com Date: Tue, 15 Aug 2017 16:20:05 +0200 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Lan Tianyu Cc: Konrad Rzeszutek Wilk , David Hildenbrand , pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM/x86: Increase max vcpu number to 352 Message-ID: <20170815142005.GA5975@flask> References: <1502359259-24966-1-git-send-email-tianyu.lan@intel.com> <20170810175056.GR2547@char.us.oracle.com> <23159a7e-463a-2a5b-5aaa-ef7f0eb43547@intel.com> <20170811130020.GB28649@flask> <20170811193531.GM32249@dhcp-amer-vpn-adc-anyconnect-10-154-152-169.vpn.oracle.com> <323bcdf0-4f4c-5c24-fe8e-f2f773b58370@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <323bcdf0-4f4c-5c24-fe8e-f2f773b58370@intel.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Tue, 15 Aug 2017 14:20:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1282 Lines: 28 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.)