From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takuya Yoshikawa Subject: Re: [PATCH 0/8] KVM: Reduce mmu_lock hold time when zapping mmu pages Date: Wed, 23 Jan 2013 22:28:46 +0900 Message-ID: <20130123222846.05bfc05a91ee133bd25981d6@gmail.com> References: <20130123191231.d66489d2.yoshikawa_takuya_b1@lab.ntt.co.jp> <50FFBF24.3000203@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Takuya Yoshikawa , mtosatti@redhat.com, gleb@redhat.com, kvm@vger.kernel.org To: Xiao Guangrong Return-path: Received: from mail-pa0-f53.google.com ([209.85.220.53]:46726 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752463Ab3AWN2u (ORCPT ); Wed, 23 Jan 2013 08:28:50 -0500 Received: by mail-pa0-f53.google.com with SMTP id hz1so4760464pad.40 for ; Wed, 23 Jan 2013 05:28:50 -0800 (PST) In-Reply-To: <50FFBF24.3000203@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, 23 Jan 2013 18:44:52 +0800 Xiao Guangrong wrote: > On 01/23/2013 06:12 PM, Takuya Yoshikawa wrote: > > This patch set mitigates another mmu_lock hold time issue. Although > > this is not enough and I'm thinking of additional work already, this > > alone can reduce the lock hold time to some extent. > > > > It is not worth doing this kind of complex thing, usually, only a few pages on > the invalid list. The *really* heavily case is kvm_mmu_zap_all() which can be speeded > up by using generation number, this is a todo work in kvm wiki: I don't think this is so complex. This is a basic programming technique using linked lists. The current code which deletes the two link nodes in different functions looks unnatural to me: traversing the sp->link nodes forces us to break the loop and sp->hash_link nodes alone is allowed to continue ... Making each function semantically clear should be more important than other things. But maybe a matter of taste, so I'll wait for the maintainers' comments. > http://www.linux-kvm.org/page/TODO: O(1) mmu invalidation using a generation number > > I am doing this work for some weeks and will post the patch out during these days. I remember that Avi originally wrote the idea of introducing the generation of mmu pages in his other work. Thanks, Takuya