From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CCA55C64E8A for ; Wed, 2 Dec 2020 12:50:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B4FF2222A for ; Wed, 2 Dec 2020 12:50:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729859AbgLBMu5 (ORCPT ); Wed, 2 Dec 2020 07:50:57 -0500 Received: from szxga03-in.huawei.com ([45.249.212.189]:2389 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727639AbgLBMu5 (ORCPT ); Wed, 2 Dec 2020 07:50:57 -0500 Received: from dggeme706-chm.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4CmJhP5YQxz50gv; Wed, 2 Dec 2020 20:49:41 +0800 (CST) Received: from [10.174.186.123] (10.174.186.123) by dggeme706-chm.china.huawei.com (10.1.199.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1913.5; Wed, 2 Dec 2020 20:50:14 +0800 Subject: Re: [PATCH v2 0/3] Fix several bugs in KVM stage 2 translation To: Marc Zyngier CC: Will Deacon , , , Catalin Marinas , James Morse , Julien Thierry , Suzuki K Poulose , Gavin Shan , Quentin Perret , , , , , , , References: <20201201201034.116760-1-wangyanan55@huawei.com> <20201201205948.GA28178@willie-the-truck> <74540986-6197-34bc-cd53-850472091ee3@huawei.com> <616980dcddd5c7e832c1068f6fa91449@kernel.org> From: "wangyanan (Y)" Message-ID: Date: Wed, 2 Dec 2020 20:50:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <616980dcddd5c7e832c1068f6fa91449@kernel.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.174.186.123] X-ClientProxiedBy: dggeme708-chm.china.huawei.com (10.1.199.104) To dggeme706-chm.china.huawei.com (10.1.199.102) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/12/2 20:23, Marc Zyngier wrote: > Hi Yanan, > > [...] > >> BTW: there are two more things below that I want to talk about. >> >> 1.  Recently, I have been focusing on the ARMv8.4-TTRem feature which >> is aimed at changing block size in stage 2 mapping. >> >> I have a plan to implement this feature for stage 2 translation when >> splitting a block into tables or merging tables into a block. >> >> This feature supports changing block size without performing >> *break-before-make*, which might have some improvement on performance. >> >> What do you think about this? > > It would be interesting if you can demonstrate some significant > performance improvements compared to the same workload with BBM. > > I'm not completely convinced this would change much, given that > it is only when moving from a table to a block mapping that you > can elide BBM when the support level is 1 or 2. As far as I can > tell, this only happens in the "stop logging" case. > > Is that something that happens often enough to justify the added > complexity? Having to handle TLB Conflict Abort is annoying, for > example. I will take more consideration about the necessity  and maybe some tests on the performance will be made later. Thanks, Yanan > >> 2. Given that the issues we discussed before were found in practice >> when guest state changes from dirty logging to dirty logging canceled. >> >> I could add a test file testing on this case to selftests/ or kvm unit >> tests/, if it's necessary. > > That would be awesome, and I'd be very grateful if you did. It is the > second time we break this exact case, and having a reliable way to > verify it would definitely help. > > Thanks, > >         M.