Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 11 Aug 2023 17:48:06 +0800
From:   Aaron Lu <aaron.lu@intel.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>,
        "Mel Gorman" <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Tim Chen <tim.c.chen@intel.com>,
        Nitin Tekchandani <nitin.tekchandani@intel.com>,
        Yu Chen <yu.c.chen@intel.com>,
        Waiman Long <longman@redhat.com>,
        <linux-kernel@vger.kernel.org>, <yury.norov@gmail.com>,
        <andriy.shevchenko@linux.intel.com>, <linux@rasmusvillemoes.dk>,
        <rppt@kernel.org>
Subject: Re: [RFC PATCH 2/4] sched/fair: Make tg->load_avg per node
Message-ID: <20230811094806.GB399195@ziqianlu-dell>
References: <20230718134120.81199-1-aaron.lu@intel.com>
 <20230718134120.81199-3-aaron.lu@intel.com>
 <20230719115358.GB3529734@hirez.programming.kicks-ass.net>
 <20230719134500.GB91858@ziqianlu-dell>
 <20230802112836.GA212435@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20230802112836.GA212435@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?nicgaEcA3qGg8Wmn46VDyrpMh++y1Mnf1kxswboLaBrr8tPNanmMdxVrs61c?=
 =?us-ascii?Q?CSZFwZk6Us2O9RJ9mS2LKXyDAtEBVaOyLQaa7ZxFK91iOu7avW+0PqgOmouH?=
 =?us-ascii?Q?4D8xQHZgj3JYwWGSSbjw3QbEUGNf1MfjDr7KHxiCU/q3+10t3fc6Wd+sB+eg?=
 =?us-ascii?Q?ZMadqe1x/x/Hl8CvtS9O9h08MFtNrLJkOYoWOqNU+qpE49zIgLpc35OHfywF?=
 =?us-ascii?Q?IRtS0iZ+YL/CO3b+ShbjsPbm/QLn1ihUyKOH8sOoz17AUbeewoRqia5KF5iZ?=
 =?us-ascii?Q?PK6EB78fjWvUhr/lfEfmXle342Xld3VTXeo2colm8f8RGG3ccqK7jL+ZCAtg?=
 =?us-ascii?Q?ZR3BN2pscvrDv/L3/70WFMcL24j0llQRLhbY2771nF04Ol6Mvp7pmKyUIjEU?=
 =?us-ascii?Q?HGGamtlCCdTVr8bhEcVu1/Cfeqk4ZhO/e1/r6D10bvyR0HSKmhl3V72iBRke?=
 =?us-ascii?Q?mZT0A1MRwdI+ibHpJ3ebkqtzTQWC0MbnUbkWm8Gz84d2nZzrHPRoupwRrZWV?=
 =?us-ascii?Q?tjpUdPjSYUUNXy5UxBru42YpOaTIRAj+4SJ9EAxBKcMqvtAIso+RmONTGR85?=
 =?us-ascii?Q?WJ2WyAs+3bqvcXkabedKiAV+/JAqs/qplc+KNFtRUiyOHHZBb/lKPVyA3x9q?=
 =?us-ascii?Q?2y+PD/r1hOf4W+aTjSsoplADtW74wF78xh40De3X8qzIJoNDz3e9CmVD5Uib?=
 =?us-ascii?Q?1Yt0jI7JRzIgPaYVlOQcFugxRvYdMm9D3vhYYHUUjyyLefdERrPvs67qua+k?=
 =?us-ascii?Q?YpJ9c5GHVK7N+lWtjmDx/Q2qxUBqh/TEvpGRUiJi+oAXkGlw2dq1JCPidn6l?=
 =?us-ascii?Q?jG3UwuZXikD70x6weLDiNY0I11dpb/vb0qTRe9Bb1roMwRH5KDZDcimDjTtO?=
 =?us-ascii?Q?W3uKhXEdIoudrDQ3ruvyjACIyY0Xebwusd4vFou2oR8pkfMzTB6NWV3nvF0P?=
 =?us-ascii?Q?ouMEau3EK5DVgYzL2Xdv0KgMUf6Y3pgCYb9wrSVYR/WY4ZY+wO6qwEnkqa+F?=
 =?us-ascii?Q?ul4Y4GuLpC5ACw9ZKiTD1fVqkQulaZTdmcLhp58jl7z0tW3vlPt9Cr3jiBLY?=
 =?us-ascii?Q?C9jm5zg7XD81oBtD/8ggrLNq8IOWIWUbtbApEwamZ4c6kQVH/f5ofIEPtngw?=
 =?us-ascii?Q?b/PIkV+I+Em3ihZcUh+F7T9nsXqUqzO2BC31eR5kk1hkIQkFW/FAuMBFvbQ7?=
 =?us-ascii?Q?KaGwl4Mqw5a199y/d0gt8UuqPpnUWkkVKgpPkpffxcBabgPF0TvTdT/0kCJB?=
 =?us-ascii?Q?jNkm2PpDjpnbM3khI5guwUdRSr5OEL/6VIMv/mZzoHIW80ONh0yg7Q51RfUE?=
 =?us-ascii?Q?mXbBsugsE6xmKB1Htj7aFZ4wk2+G9vEQkx2cI/U5y85Jtn+INJI3lFBOvMYh?=
 =?us-ascii?Q?Gtl/GZl5WjezU48mWfIL1+rd+osLcfJrjnuWs8SPwvR3WlZTj0kY6NE7SrSV?=
 =?us-ascii?Q?yA0rWuZvHRrkcXoBYY0EX+oFA80LsKZdB/q9dnwhE6DGjYMNfDXkrHdJFb9L?=
 =?us-ascii?Q?Q12AKyHB8OTNQTaTK58VR02GWI7qv4fzbB+yPB8BfbVv1D9M6+QveEG2HHv9?=
 =?us-ascii?Q?yQxpPsc6pOX2LHdMQDbzARnoTwJNmQ5e87VHN0Qq?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 35d9fae7-201a-4db4-5d7f-08db9a501983
X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3062.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Aug 2023 09:48:22.1292
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: RAl3J9Vu6MSFLaPkM/kNQlPEB8g2yMhg55rLft45IJvAUV1gEgeJgvYjnx1MIBLWdENgZvKDcs98sukiwqwOIw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY5PR11MB6091
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,
        RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_NONE,URIBL_BLOCKED
        autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Aug 02, 2023 at 01:28:36PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 19, 2023 at 09:45:00PM +0800, Aaron Lu wrote:
> > On Wed, Jul 19, 2023 at 01:53:58PM +0200, Peter Zijlstra wrote:
> > > On Tue, Jul 18, 2023 at 09:41:18PM +0800, Aaron Lu wrote:
> > > > +#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
> > > > +static inline long tg_load_avg(struct task_group *tg)
> > > > +{
> > > > +	long load_avg = 0;
> > > > +	int i;
> > > > +
> > > > +	/*
> > > > +	 * The only path that can give us a root_task_group
> > > > +	 * here is from print_cfs_rq() thus unlikely.
> > > > +	 */
> > > > +	if (unlikely(tg == &root_task_group))
> > > > +		return 0;
> > > > +
> > > > +	for_each_node(i)
> > > > +		load_avg += atomic_long_read(&tg->node_info[i]->load_avg);
> > > > +
> > > > +	return load_avg;
> > > > +}
> > > > +#endif
> > > 
> > > So I was working on something else numa and noticed that for_each_node()
> > > (and most of the nodemask stuff) is quite moronic, afaict we should do
> > > something like the below.
> > > 
> > > I now see Mike added the nr_node_ids thing fairly recent, but given
> > > distros have NODES_SHIFT=10 and actual machines typically only have <=4
> > > nodes, this would save a factor of 256 scanning.
> 
> More complete nodemask patch here:
> 
>   https://lkml.kernel.org/r/20230802112458.230221601%40infradead.org

Thanks for the update.

I incorperated this numa change and collected some data and found that
with the newly proposed approach to rate limit updates to tg->load_avg
to at most once per ms, the cost of accessing tg->load_avg is dropped
so much that adding other optimizations doesn't make much difference.

So I was thinking maybe I just need that one ratelimit patch to reduce
the cost of accessing tg->load_avg. The detailed data is here:
https://lore.kernel.org/lkml/20230811092811.GA399195@ziqianlu-dell/