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=-8.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 3BF02C004C9 for ; Tue, 7 May 2019 18:57:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E8332054F for ; Tue, 7 May 2019 18:57:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727330AbfEGS5V (ORCPT ); Tue, 7 May 2019 14:57:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56344 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726321AbfEGS5V (ORCPT ); Tue, 7 May 2019 14:57:21 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A0C2A3082E51; Tue, 7 May 2019 18:57:20 +0000 (UTC) Received: from amt.cnet (ovpn-112-11.gru2.redhat.com [10.97.112.11]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0C41F1837C; Tue, 7 May 2019 18:57:18 +0000 (UTC) Received: from amt.cnet (localhost [127.0.0.1]) by amt.cnet (Postfix) with ESMTP id 53394105182; Tue, 7 May 2019 15:56:59 -0300 (BRT) Received: (from marcelo@localhost) by amt.cnet (8.14.7/8.14.7/Submit) id x47IusZB029563; Tue, 7 May 2019 15:56:54 -0300 Date: Tue, 7 May 2019 15:56:49 -0300 From: Marcelo Tosatti To: kvm-devel , linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Andrea Arcangeli , Bandan Das , Paolo Bonzini Subject: [PATCH] sched: introduce configurable delay before entering idle Message-ID: <20190507185647.GA29409@amt.cnet> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="lrZ03NoBR/3+SXJZ" Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Tue, 07 May 2019 18:57:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --lrZ03NoBR/3+SXJZ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Certain workloads perform poorly on KVM compared to baremetal due to baremetal's ability to perform mwait on NEED_RESCHED bit of task flags (therefore skipping the IPI). This patch introduces a configurable busy-wait delay before entering the architecture delay routine, allowing wakeup IPIs to be skipped (if the IPI happens in that window). The real-life workload which this patch improves performance is SAP HANA (by 5-10%) (for which case setting idle_spin to 30 is sufficient). This patch improves the attached server.py and client.py example as follows: Host: 31.814230202231556 Guest: 38.17718765199993 (83 %) Guest, idle_spin=50us: 33.317709898000004 (95 %) Guest, idle_spin=220us: 32.27826551499999 (98 %) Signed-off-by: Marcelo Tosatti --- kernel/sched/idle.c | 86 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index f5516bae0c1b..bca7656a7ea0 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -216,6 +216,29 @@ static void cpuidle_idle_call(void) rcu_idle_exit(); } +static unsigned int spin_before_idle_us; +static void do_spin_before_idle(void) +{ + ktime_t now, end_spin; + + now = ktime_get(); + end_spin = ktime_add_ns(now, spin_before_idle_us*1000); + + rcu_idle_enter(); + local_irq_enable(); + stop_critical_timings(); + + do { + cpu_relax(); + now = ktime_get(); + } while (!tif_need_resched() && ktime_before(now, end_spin)); + + start_critical_timings(); + rcu_idle_exit(); + local_irq_disable(); +} + /* * Generic idle loop implementation * @@ -259,6 +282,8 @@ static void do_idle(void) tick_nohz_idle_restart_tick(); cpu_idle_poll(); } else { + if (spin_before_idle_us) + do_spin_before_idle(); cpuidle_idle_call(); } arch_cpu_idle_exit(); @@ -465,3 +490,64 @@ const struct sched_class idle_sched_class = { .switched_to = switched_to_idle, .update_curr = update_curr_idle, }; + + +static ssize_t store_idle_spin(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned int val; + + if (kstrtouint(buf, 10, &val) < 0) + return -EINVAL; + + if (val > USEC_PER_SEC) + return -EINVAL; + + spin_before_idle_us = val; + return count; +} + +static ssize_t show_idle_spin(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + ssize_t ret; + + ret = sprintf(buf, "%d\n", spin_before_idle_us); + + return ret; +} + +static struct kobj_attribute idle_spin_attr = + __ATTR(idle_spin, 0644, show_idle_spin, store_idle_spin); + +static struct attribute *sched_attrs[] = { + &idle_spin_attr.attr, + NULL, +}; + +static const struct attribute_group sched_attr_group = { + .attrs = sched_attrs, +}; + +static struct kobject *sched_kobj; + +static int __init sched_sysfs_init(void) +{ + int error; + + sched_kobj = kobject_create_and_add("sched", kernel_kobj); + if (!sched_kobj) + return -ENOMEM; + + error = sysfs_create_group(sched_kobj, &sched_attr_group); + if (error) + goto err; + return 0; + +err: + kobject_put(sched_kobj); + return error; +} +postcore_initcall(sched_sysfs_init); --lrZ03NoBR/3+SXJZ Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="client.py" #!/bin/python3 import socket import sys import struct, fcntl, os import os, errno, time import time sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server_address = ('127.0.0.1', 999) print ("connecting to 127.0.0.1") sock.connect(server_address) nr_writes = 0 start_time = time.clock_gettime(time.CLOCK_MONOTONIC) while nr_writes < 90000: data = sock.recv(4096) if len(data) == 0: print("connection closed!\n"); exit(0); # sleep 20us time.sleep(20/1000000) sock.send(data) nr_writes = nr_writes+1 end_time = time.clock_gettime(time.CLOCK_MONOTONIC) delta = end_time - start_time print(delta) --lrZ03NoBR/3+SXJZ Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="server.py" #!/bin/python3 import socket import sys import struct, fcntl, os import os, errno, time import time sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.bind(('127.0.0.1', 999)) sock.listen(10) conn, addr = sock.accept() nr_written=0 while 1: conn.sendall(b"a response line of text") data = conn.recv(1024) if not data: break # sleep 200us time.sleep(200/1000000) nr_written = nr_written+1 --lrZ03NoBR/3+SXJZ--