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=-8.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 DE793C636CA for ; Fri, 16 Jul 2021 21:12:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAE9261380 for ; Fri, 16 Jul 2021 21:12:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234967AbhGPVPR (ORCPT ); Fri, 16 Jul 2021 17:15:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:24145 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230084AbhGPVPQ (ORCPT ); Fri, 16 Jul 2021 17:15:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626469940; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rtZkPkL5ifGn/qh+FLZXpXfgaKHtHcJkyP1xEcuftv4=; b=KkW+SA8tFpNkmU5hsmDl/JYC2RyWOByOFDxb1g2Iyz5nAUd+9RVJNkCmLz7I68H9ON2dAC Fpwax3bLaPcLuZiSfJ7FrB/lQKrg8YdqMBXYF8uOEC8oSpGm57NbUs7ZT9/os/ABug5FnR pxRZvYSEY16nc4Nm8rYvOmrpxmPT9js= Received: from mail-qv1-f69.google.com (mail-qv1-f69.google.com [209.85.219.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-322-TA52KyN7PpqXWmRJ6Iu12g-1; Fri, 16 Jul 2021 17:12:19 -0400 X-MC-Unique: TA52KyN7PpqXWmRJ6Iu12g-1 Received: by mail-qv1-f69.google.com with SMTP id c5-20020a0562141465b02902e2f9404330so7589148qvy.9 for ; Fri, 16 Jul 2021 14:12:19 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=rtZkPkL5ifGn/qh+FLZXpXfgaKHtHcJkyP1xEcuftv4=; b=Iu8XKp9zPyJmqToFOUN6wY8n1nRHjoxUNQo1endS13WZCPMXbWa9Jq4Wikt6YjD7MH r6rW4IX/1lBtLNoSyGtbpYANmfVvG9V4v+TDPyxF6ok85W4q+u97mwH7Lyo5LhQnzKX8 PhtN3JsnYUlQRRapvo3gTc69lmuWeV2IaUVQkZLM0GkyGDWXJ2I8jnr+v7Qt1EYvdl4h zAxj2rHwc14n6wndPd7HgzebJmOnL1ybRA1QTbIbX2iR1+ZdrLu14OglPHb47S0WZfbB jFGSqGmsvMbX14sG3Un7IoixLXIEQEQiQDqt+3Kj1JBpYp/17Fy5GC3Ovv/ZZDqVY9HO xzHQ== X-Gm-Message-State: AOAM533cGWEI9ApWM4a6ocY4dWTaBjaWaVhIasqnbFzewbeQPdBodzY7 CM8o5odJH8jVclNsaWqChSd1uSxU7VYHFSMk8Cwh6WZXQxrHuJLKYQBoqhCcVkKCOrKan13v4zD 5+PJCN4CNbYiRdw/mugd50UTY X-Received: by 2002:ae9:e511:: with SMTP id w17mr11949834qkf.306.1626469939102; Fri, 16 Jul 2021 14:12:19 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx9mVFlRQajFH1fN2NUgEKxwR2UFx9GsK1tedNLIEIZuzRTR9mkQNQGf6W+FM+nKWayRyhUCA== X-Received: by 2002:ae9:e511:: with SMTP id w17mr11949813qkf.306.1626469938928; Fri, 16 Jul 2021 14:12:18 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id r187sm4315358qkb.129.2021.07.16.14.12.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 16 Jul 2021 14:12:18 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH v2 2/6] cgroup/cpuset: Clarify the use of invalid partition root To: Tejun Heo , Waiman Long Cc: Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli References: <20210621184924.27493-1-longman@redhat.com> <20210621184924.27493-3-longman@redhat.com> <6ea1ac38-73e1-3f78-a5d2-a4c23bcd8dd1@redhat.com> <1bb119a1-d94a-6707-beac-e3ae5c03fae5@redhat.com> <8c44b659-3fe4-b14f-fac1-cbd5b23010c3@redhat.com> Message-ID: Date: Fri, 16 Jul 2021 17:12:17 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/16/21 4:46 PM, Tejun Heo wrote: > Hello, Waiman. > > On Fri, Jul 16, 2021 at 04:08:15PM -0400, Waiman Long wrote: >>>> I agree with you on principle. However, the reason why there are >>>> more restrictions on enabling partition is because I want to avoid >>>> forcing the users to always read back cpuset.partition.type to see >>>> if the operation succeeds instead of just getting an error from the >>>> operation. The former approach is more error prone. If you don't >>>> want changes in existing behavior, I can relax the checking and >>>> allow them to become an invalid partition if an illegal operation >>>> happens. >>>> >>>> Also there is now another cpuset patch to extend cpu isolation to >>>> cgroup v1 [1]. I think it is better suit to the cgroup v2 partition >>>> scheme, but cgroup v1 is still quite heavily out there. >>>> >>>> Please let me know what you want me to do and I will send out a v3 >>>> version. >>> Note that the current cpuset partition implementation have implemented >>> some restrictions on when a partition can be enabled. However, I missed >>> some corner cases in the original implementation that allow certain >>> cpuset operations to make a partition invalid. I tried to plug those >>> holes in this patchset. However, if maintaining backward compatibility >>> is more important, I can leave those holes and update the documentation >>> to make sure that people check cpuset.partition.type to confirm if their >>> operation succeeds. >> I just realize that partition root set the CPU_EXCLUSIVE bit. So changes to >> cpuset.cpus that break exclusivity rule is not allowed anyway. This patchset >> is just adding additional checks so that cpuset.cpus changes that break the >> partition root rules will not be allowed. I can remove those additional >> checks for this patchset and allow cpuset.cpus changes that break the >> partition root rules to make it invalid instead. However, I still want >> invalid changes to cpuset.partition.type to be disallowed. > So, I get the instinct to disallow these operations and it'd make sense if > the conditions aren't reachable otherwise. However, I'm afraid what users > eventually get is false sense of security rather than any actual guarantee. > > Inconsistencies like this cause actual usability hazards - e.g. imagine a > system config script whic sets up exclusive cpuset and let's say that the > use case is fine with degraded operation when the target cores are offline > (e.g. energy save mode w/ only low power cores online). Let's say this > script runs in late stages during boot and has been reliable. However, at > some point, there are changes in boot sequence and now there's low but > non-trivial chance that the system would already be in low power state when > the script runs. Now the script will fail sporadically and the whole thing > would be pretty awkward to debug. > > I'd much prefer to have an explicit interface to confirm the eventual state > and a way to monitor state transitions (without polling). An invalid state > is an inherent part of cpuset configuration. I'd much rather have that > really explicit in the interface even if that means a bit of extra work at > configuration time. Are you suggesting that we add a cpuset.cpus.events file that allows processes to be notified if an event (e.g. hotplug) that changes a partition root to invalid partition happens or when explicit change to a partition root fails? Will that be enough to satisfy your requirement? Cheers, Longman From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v2 2/6] cgroup/cpuset: Clarify the use of invalid partition root Date: Fri, 16 Jul 2021 17:12:17 -0400 Message-ID: References: <20210621184924.27493-1-longman@redhat.com> <20210621184924.27493-3-longman@redhat.com> <6ea1ac38-73e1-3f78-a5d2-a4c23bcd8dd1@redhat.com> <1bb119a1-d94a-6707-beac-e3ae5c03fae5@redhat.com> <8c44b659-3fe4-b14f-fac1-cbd5b23010c3@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626469941; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rtZkPkL5ifGn/qh+FLZXpXfgaKHtHcJkyP1xEcuftv4=; b=WszPjFD71SjhDDskK8JsnI+gGp5Hiung2ko2vbyqc1FIpT+r34vD/VVRnr4eDbDxoKWLk6 XHzuTEX/vkAomrobyo5wsyPrxNJhr1Ur2cnUnIpIhK0pzJK+ZzgSfS4Kdt6sxRZDSBxDs5 catWfdZTPMb4lNp6rI2fnbiKUxYX/ic= In-Reply-To: Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Tejun Heo , Waiman Long Cc: Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli On 7/16/21 4:46 PM, Tejun Heo wrote: > Hello, Waiman. > > On Fri, Jul 16, 2021 at 04:08:15PM -0400, Waiman Long wrote: >>>> I agree with you on principle. However, the reason why there are >>>> more restrictions on enabling partition is because I want to avoid >>>> forcing the users to always read back cpuset.partition.type to see >>>> if the operation succeeds instead of just getting an error from the >>>> operation. The former approach is more error prone. If you don't >>>> want changes in existing behavior, I can relax the checking and >>>> allow them to become an invalid partition if an illegal operation >>>> happens. >>>> >>>> Also there is now another cpuset patch to extend cpu isolation to >>>> cgroup v1 [1]. I think it is better suit to the cgroup v2 partition >>>> scheme, but cgroup v1 is still quite heavily out there. >>>> >>>> Please let me know what you want me to do and I will send out a v3 >>>> version. >>> Note that the current cpuset partition implementation have implemented >>> some restrictions on when a partition can be enabled. However, I missed >>> some corner cases in the original implementation that allow certain >>> cpuset operations to make a partition invalid. I tried to plug those >>> holes in this patchset. However, if maintaining backward compatibility >>> is more important, I can leave those holes and update the documentation >>> to make sure that people check cpuset.partition.type to confirm if their >>> operation succeeds. >> I just realize that partition root set the CPU_EXCLUSIVE bit. So changes to >> cpuset.cpus that break exclusivity rule is not allowed anyway. This patchset >> is just adding additional checks so that cpuset.cpus changes that break the >> partition root rules will not be allowed. I can remove those additional >> checks for this patchset and allow cpuset.cpus changes that break the >> partition root rules to make it invalid instead. However, I still want >> invalid changes to cpuset.partition.type to be disallowed. > So, I get the instinct to disallow these operations and it'd make sense if > the conditions aren't reachable otherwise. However, I'm afraid what users > eventually get is false sense of security rather than any actual guarantee. > > Inconsistencies like this cause actual usability hazards - e.g. imagine a > system config script whic sets up exclusive cpuset and let's say that the > use case is fine with degraded operation when the target cores are offline > (e.g. energy save mode w/ only low power cores online). Let's say this > script runs in late stages during boot and has been reliable. However, at > some point, there are changes in boot sequence and now there's low but > non-trivial chance that the system would already be in low power state when > the script runs. Now the script will fail sporadically and the whole thing > would be pretty awkward to debug. > > I'd much prefer to have an explicit interface to confirm the eventual state > and a way to monitor state transitions (without polling). An invalid state > is an inherent part of cpuset configuration. I'd much rather have that > really explicit in the interface even if that means a bit of extra work at > configuration time. Are you suggesting that we add a cpuset.cpus.events file that allows processes to be notified if an event (e.g. hotplug) that changes a partition root to invalid partition happens or when explicit change to a partition root fails? Will that be enough to satisfy your requirement? Cheers, Longman