From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755524AbaFYIuN (ORCPT ); Wed, 25 Jun 2014 04:50:13 -0400 Received: from mga03.intel.com ([143.182.124.21]:15737 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755610AbaFYIjk (ORCPT ); Wed, 25 Jun 2014 04:39:40 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,544,1400050800"; d="scan'208";a="449717389" From: Yuyang Du To: mingo@redhat.com, peterz@infradead.org, rafael.j.wysocki@intel.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Cc: arjan.van.de.ven@intel.com, len.brown@intel.com, alan.cox@intel.com, mark.gross@intel.com, morten.rasmussen@arm.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rajeev.d.muralidhar@intel.com, vishwesh.m.rudramuni@intel.com, nicole.chalhoub@intel.com, ajaya.durg@intel.com, harinarayanan.seshadri@intel.com, jacob.jun.pan@linux.intel.com, Yuyang Du Subject: =?UTF-8?q?=5BRFC=20PATCH=200/9=20v4=5D=20A=20new=20CPU=20load=20metric=20for=20power-efficient=20scheduler=3A=20CPU=20ConCurrency?= Date: Wed, 25 Jun 2014 08:35:59 +0800 Message-Id: <1403656568-32445-1-git-send-email-yuyang.du@intel.com> X-Mailer: git-send-email 1.7.9.5 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The current scheduler’s load balancing is completely work-conserving. In some workload, generally low CPU utilization but immersed with CPU bursts of transient tasks, migrating task to engage all available CPUs for work-conserving can lead to significant overhead: cache locality loss, idle/active HW state transitional latency and power, shallower idle state, etc, which are both power and performance inefficient especially for today’s low power processors in mobile. This RFC introduces a sense of idleness-conserving into work-conserving (by all means, we really don’t want to be overwhelming in only one way). But to what extent the idleness-conserving should be, bearing in mind that we don’t want to sacrifice performance? We first need a load/idleness indicator to that end. Thanks to CFS’s “model an ideal, precise multi-tasking CPU”, tasks can be seen as concurrently running (the tasks in the runqueue). So it is natural to use task concurrency as load indicator. Having said that, we do two things: 1) Divide continuous time into periods of time, and average task concurrency in period, for tolerating the transient bursts: a = sum(concurrency * time) / period 2) Exponentially decay past periods, and synthesize them all, for hysteresis to load drops or resilience to load rises (let f be decaying factor, and a_x the xth period average since period 0): s = a_n + f^1 * a_n-1 + f^2 * a_n-2 +, ..., + f^(n-1) * a_1 + f^n * a_0 We name this load indicator as CPU ConCurrency (CC): task concurrency determines how many CPUs are needed to be running concurrently. Another two ways of how to interpret CC: 1) the current work-conserving load balance also uses CC, but instantaneous CC. 2) CC vs. CPU utilization. CC is runqueue-length-weighted CPU utilization. If we change: "a = sum(concurrency * time) / period" to "a' = sum(1 * time) / period". Then a' is just about the CPU utilization. And the way we weight runqueue-length is the simplest one (excluding the exponential decays, and you may have other ways). To track CC, we intercept the scheduler in 1) enqueue, 2) dequeue, 3) scheduler tick, and 4) enter/exit idle. After CC, in the consolidation part, we do 1) attach the CPU topology to be adaptive beyond our experimental platforms, and 2) intercept the current load balance for load and load balancing containment. Currently, CC is per CPU. To consolidate, the formula is based on a heuristic. Suppose we have 2 CPUs, their task concurrency over time is ('-' means no task, 'x' having tasks): 1) CPU0: ---xxxx---------- (CC[0]) CPU1: ---------xxxx---- (CC[1]) 2) CPU0: ---xxxx---------- (CC[0]) CPU1: ---xxxx---------- (CC[1]) If we consolidate CPU0 and CPU1, the consolidated CC will be: CC' = CC[0] + CC[1] for case 1 and CC'' = (CC[0] + CC[1]) * 2 for case 2. For the cases in between case 1 and 2 in terms of how xxx overlaps, the CC should be between CC' and CC''. So, we uniformly use this condition for consolidation (suppose we consolidate m CPUs to n CPUs, m > n): (CC[0] + CC[1] + ... + CC[m-2] + CC[m-1]) * (n + log(m-n)) >=avg first, and base our patch on it - Removed all CONFIG_CPU_CONCURRENCY and CONFIG_WORKLOAD_CONSOLIDATION - CPU CC will be updated mandatory - CPU WC can be enabled/disabled by flags per domain level on the fly - CPU CC and WC is completely fair scheduler thing, don't touch RT anymore v2: - Data type defined in formation Patchset against linux-next v3.16-rc2. Yuyang Du (9): sched: Remove update_rq_runnable_avg sched: Precise accumulated time and acount runnable number in update_entity_runnable_avg How CPU ConCurrency (CC) accrues with runqueue change and time Define SD_WORKLOAD_CONSOLIDATION and attach to sched_domain Workload Consolidation: Consolidating workload to a subset of CPUs if possible Implement Workload Consolidation in wakeup/fork/exec Implement Workload Consolidation in idle_balance Implement Workload Consolidation in nohz_idle_balance Implement Workload Consolidation in periodic load balance include/linux/sched.h | 9 +- include/linux/sched/sysctl.h | 4 + kernel/sched/core.c | 46 +++- kernel/sched/debug.c | 8 - kernel/sched/fair.c | 576 +++++++++++++++++++++++++++++++++++++++--- kernel/sched/sched.h | 17 +- kernel/sysctl.c | 9 + 7 files changed, 612 insertions(+), 57 deletions(-) -- 1.7.9.5