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[2620:137:e000::1:20]) by mx.google.com with ESMTP id ga25-20020a170906b85900b009272e9ad68fsi8229341ejb.548.2023.03.22.02.40.55; Wed, 22 Mar 2023 02:41:18 -0700 (PDT) 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; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=mXoIuD2v; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230346AbjCVJXQ (ORCPT + 99 others); Wed, 22 Mar 2023 05:23:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229872AbjCVJXI (ORCPT ); Wed, 22 Mar 2023 05:23:08 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A82D5070C; Wed, 22 Mar 2023 02:22:27 -0700 (PDT) Date: Wed, 22 Mar 2023 09:22:24 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1679476945; h=from:from:sender:sender:reply-to: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=1HcTumDeaE8hefYvRKp1CarUG+FHryAI2Op27a6IOj0=; b=mXoIuD2vOZBuvdOrnRmtHPTnsw0NV6NFwAZw+jlUWOuPaus89B35wQlFeIxSw7ELyxRjQS jWvvXpGrPlI5aNBGxjBnP+O8M4d4dkYAmc36HYyMLZzLxZ8jLClemYWNuGDVp5eXXTd3g1 wnxWAmUDZ51zSAirliPVtrX05rabniticwo7i1V6+DVTB+RSJKsJIpk3z1r2zcjHqPMWKi 8vJ2h89bGKBS0M+Gdu+n5gajy3Ty6FeZR9OhWMhQEdqCIv0fRKtriiM1UhXo2xuK1QtZUF Gpn9HDiRxyBh/EkgevX+VCFQZLubEQbKqvs4pZgrgGXd6g8irA5JBzV45W60gQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1679476945; h=from:from:sender:sender:reply-to: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=1HcTumDeaE8hefYvRKp1CarUG+FHryAI2Op27a6IOj0=; b=D0pg/5I8vJwZWt7VtxCtFNKDz/e6p2QbvSXA7TseYJHrMwhx2lN9zZ3zv7dS7ZRhVGINwy udGBgGbHkW+x6sDw== From: "tip-bot2 for Shrikanth Hegde" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: Interleave cfs bandwidth timers for improved single thread performance at low utilization Cc: Peter Zijlstra , Thomas Gleixner , Shrikanth Hegde , Ben Segall , Vincent Guittot , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230223185153.1499710-1-sshegde@linux.vnet.ibm.com> References: <20230223185153.1499710-1-sshegde@linux.vnet.ibm.com> MIME-Version: 1.0 Message-ID: <167947694435.5837.4783661617019925229.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails X-Spam-Status: No, score=-2.5 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1761060405994028116?= X-GMAIL-MSGID: =?utf-8?q?1761060405994028116?= The following commit has been merged into the sched/core branch of tip: Commit-ID: 41abdba9374734b743019fc1cc05e3225c82ba6b Gitweb: https://git.kernel.org/tip/41abdba9374734b743019fc1cc05e3225c82ba6b Author: Shrikanth Hegde AuthorDate: Fri, 24 Feb 2023 00:21:53 +05:30 Committer: Peter Zijlstra CommitterDate: Wed, 22 Mar 2023 10:10:58 +01:00 sched: Interleave cfs bandwidth timers for improved single thread performance at low utilization CPU cfs bandwidth controller uses hrtimer. Currently there is no initial value set. Hence all period timers would align at expiry. This happens when there are multiple CPU cgroup's. There is a performance gain that can be achieved here if the timers are interleaved when the utilization of each CPU cgroup is low and total utilization of all the CPU cgroup's is less than 50%. If the timers are interleaved, then the unthrottled cgroup can run freely without many context switches and can also benefit from SMT Folding. This effect will be further amplified in SPLPAR environment. This commit adds a random offset after initializing each hrtimer. This would result in interleaving the timers at expiry, which helps in achieving the said performance gain. This was tested on powerpc platform with 8 core SMT=8. Socket power was measured when the workload. Benchmarked the stress-ng with power information. Throughput oriented benchmarks show significant gain up to 25% while power consumption increases up to 15%. Workload: stress-ng --cpu=32 --cpu-ops=50000. 1CG - 1 cgroup is running. 2CG - 2 cgroups are running together. Time taken to complete stress-ng in seconds and power is in watts. each cgroup is throttled at 25% with 100ms as the period value. 6.2-rc6 | with patch 8 core 1CG power 2CG power | 1CG power 2 CG power 27.5 80.6 40 90 | 27.3 82 32.3 104 27.5 81 40.2 91 | 27.5 81 38.7 96 27.7 80 40.1 89 | 27.6 80 29.7 106 27.7 80.1 40.3 94 | 27.6 80 31.5 105 Latency might be affected by this change. That could happen if the CPU was in a deep idle state which is possible if we interleave the timers. Used schbench for measuring the latency. Each cgroup is throttled at 25% with period value is set to 100ms. Numbers are when both the cgroups are running simultaneously. Latency values don't degrade much. Some improvement is seen in tail latencies. 6.2-rc6 with patch Groups: 16 50.0th: 39.5 42.5 75.0th: 924.0 922.0 90.0th: 972.0 968.0 95.0th: 1005.5 994.0 99.0th: 4166.0 2287.0 99.5th: 7314.0 7448.0 99.9th: 15024.0 13600.0 Groups: 32 50.0th: 819.0 463.0 75.0th: 1596.0 918.0 90.0th: 5992.0 1281.5 95.0th: 13184.0 2765.0 99.0th: 21792.0 14240.0 99.5th: 25696.0 18920.0 99.9th: 33280.0 35776.0 Groups: 64 50.0th: 4806.0 3440.0 75.0th: 31136.0 33664.0 90.0th: 54144.0 58752.0 95.0th: 66176.0 67200.0 99.0th: 84736.0 91520.0 99.5th: 97408.0 114048.0 99.9th: 136448.0 140032.0 Initial RFC PATCH, discussions and details on the problem: Link1: https://lore.kernel.org/lkml/5ae3cb09-8c9a-11e8-75a7-cc774d9bc283@linux.vnet.ibm.com/ Link2: https://lore.kernel.org/lkml/9c57c92c-3e0c-b8c5-4be9-8f4df344a347@linux.vnet.ibm.com/ Suggested-by: Peter Zijlstra Suggested-by: Thomas Gleixner Signed-off-by: Shrikanth Hegde Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ben Segall Reviewed-by: Vincent Guittot Link: https://lore.kernel.org/r/20230223185153.1499710-1-sshegde@linux.vnet.ibm.com --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b572367..bc358dc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5923,6 +5923,10 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq); hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED); cfs_b->period_timer.function = sched_cfs_period_timer; + + /* Add a random offset so that timers interleave */ + hrtimer_set_expires(&cfs_b->period_timer, + get_random_u32_below(cfs_b->period)); hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); cfs_b->slack_timer.function = sched_cfs_slack_timer; cfs_b->slack_started = false;