Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757227AbZF3Wkb (ORCPT ); Tue, 30 Jun 2009 18:40:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753439AbZF3WkV (ORCPT ); Tue, 30 Jun 2009 18:40:21 -0400 Received: from one.firstfloor.org ([213.235.205.2]:54034 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752569AbZF3WkU (ORCPT ); Tue, 30 Jun 2009 18:40:20 -0400 Date: Wed, 1 Jul 2009 00:40:18 +0200 From: Andi Kleen To: Ingo Molnar Cc: Christoph Lameter , Andrew Morton , tj@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, andi@firstfloor.org, hpa@zytor.com, tglx@linutronix.de Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and improve lpage NUMA support Message-ID: <20090630224018.GJ6760@one.firstfloor.org> References: <1245850216-31653-1-git-send-email-tj@kernel.org> <20090624165508.30b88343.akpm@linux-foundation.org> <20090629163937.94c8cedd.akpm@linux-foundation.org> <20090630191517.GB20567@elte.hu> <20090630213146.GA17492@elte.hu> <20090630223138.GH1241@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090630223138.GH1241@elte.hu> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1239 Lines: 29 > How would you allow that guest to stay on 2 virtual CPUs but still > be able to hot-plug many other CPUs if the guest context rises above > its original CPU utilization? (unless you're planning to rewrite lots of possible cpu users all over the tree) -- the only way is to keep the percpu area small and preallocate. As long as the per cpu data size stays reasonable (not more than a 100-200k) that's very doable. It probably won't work with 4096 guest CPUs without wasting too much memory, but then I don't think we have any Hypervisor that scales to that many CPUs anyways, so it's not the biggest concern. For the 128CPU case it works (although i might need to enlarge vmalloc area a bit on 32bit) Unfortunately a few debugging subsystems seem to currently eat much more, but those just need to be fixed to only allocate state for actually running CPUs, not just possible ones. I suspect we need a scripts/percpubloat.pl -Andi -- ak@linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/