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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 E63BFC47081 for ; Sun, 23 May 2021 13:35:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B15A0611CA for ; Sun, 23 May 2021 13:35:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231792AbhEWN2J (ORCPT ); Sun, 23 May 2021 09:28:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:39092 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231757AbhEWN2I (ORCPT ); Sun, 23 May 2021 09:28:08 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AEEC661152; Sun, 23 May 2021 13:26:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1621776402; bh=x9fa6LhWXf5Omps2BCm9Zi0bMDKuatQdsTMAYYWldFQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iXJ4BRBZQJ4BtSsosxLwZk3iO+2bBKM/tvRZQKI69nRobffcwH09SGxKoo50oV05e 0nIERyRpWG1LQ8rcHM/do1RyvMhqNE005ycSTP2wXP5LoKxc0qcW9SzuqdN5eKTIQv niYq6YUYjCOAk+w1Rp9LsJKB4IaZ0+vftfGEipmFwAOlPu5CDMmqq5zJqkzuc5FjcD okxWjWnkGFr8yfGjZ7sOmhgjXdqiZ2oApyrvb27SRpptce6MZ/SCUVr6tEEJeXuhKv uMGPAUzTFaznkA67VAlXNhQWn0eoNk1Y5BdJOQhsrOmaDeB2rYYcdlXYCubMriENdw M5utK8w0eWmbw== Date: Sun, 23 May 2021 15:26:39 +0200 From: Frederic Weisbecker To: Oliver Sang Cc: Peter Zijlstra , "Paul E. McKenney" , Ingo Molnar , LKML , lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com, feng.tang@intel.com, zhengjun.xing@intel.com Subject: Re: [entry] 47b8ff194c: will-it-scale.per_process_ops -3.0% regression Message-ID: <20210523132639.GB173496@lothringen> References: <20210428071653.GC13086@xsang-OptiPlex-9020> <20210513174636.GB975577@paulmck-ThinkPad-P17-Gen-1> <20210513231127.GA165500@lothringen> <20210519052700.GC29704@xsang-OptiPlex-9020> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210519052700.GC29704@xsang-OptiPlex-9020> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 19, 2021 at 01:27:00PM +0800, Oliver Sang wrote: > hi, Peter Zijlstra, > > On Fri, May 14, 2021 at 12:13:22PM +0200, Peter Zijlstra wrote: > > On Fri, May 14, 2021 at 01:11:27AM +0200, Frederic Weisbecker wrote: > > > > > That sounds good, but two things: > > > > > > 1) Even if context tracking is not running, we still need to handle > > > deferred wakeups on idle. But all user/guest/idle currently use the > > > same function. > > > > > > 2) Context tracking may be running even when full nohz is not. But here only > > > full nohz is concerned. > > > > > > So the change should rather be as follows (completely untested!). > > > I rather put the static key check in tick.h in order not to involve > > > deep dependencies inside rcupdate.h (especially rcupdate.h -> tick.h -> sched.h) > > > > Compiles and boots for me, 0day folks, could you please test this makes > > the reported regression go away? > > sorry for late. > > on which base should we apply below patch? > we tried to apply upon 4ae7dc97f726e ("entry/kvm: Explicitly flush pending rcuog > wakeup before last rescheduling point") and v5.12, but both build failed like below: > > ERROR: modpost: "tick_nohz_full_mask" [arch/x86/kvm/kvm.ko] undefined! > > or is there any particular kconfig need to enable? > (the kconfig which we used to build 47b8ff194c is in original report > which maybe you could help have a look what we may miss) Ah indeed I need to export tick_nohz_full_mask. Too bad but that's the fate of many cpu masks anyway. Can you try the following patch instead? It boots and seem to behave: --- From: Frederic Weisbecker Date: Sun, 23 May 2021 14:23:30 +0200 Subject: [PATCH] tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed Checking for and processing RCU-nocb deferred wakeup upon user/guest entry is only relevant when nohz_full runs on the local CPU, otherwise the periodic tick should take care of it. Make sure we don't needlessly pollute these fast-paths. Reported-by: kernel test robot Signed-off-by: Frederic Weisbecker --- include/linux/entry-kvm.h | 3 ++- include/linux/tick.h | 7 +++++++ kernel/entry/common.c | 5 +++-- kernel/time/tick-sched.c | 1 + 4 files changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h index 8b2b1d68b954..136b8d97d8c0 100644 --- a/include/linux/entry-kvm.h +++ b/include/linux/entry-kvm.h @@ -3,6 +3,7 @@ #define __LINUX_ENTRYKVM_H #include +#include /* Transfer to guest mode work */ #ifdef CONFIG_KVM_XFER_TO_GUEST_WORK @@ -57,7 +58,7 @@ int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu); static inline void xfer_to_guest_mode_prepare(void) { lockdep_assert_irqs_disabled(); - rcu_nocb_flush_deferred_wakeup(); + tick_nohz_user_enter_prepare(); } /** diff --git a/include/linux/tick.h b/include/linux/tick.h index 7340613c7eff..1a0ff88fa107 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -11,6 +11,7 @@ #include #include #include +#include #ifdef CONFIG_GENERIC_CLOCKEVENTS extern void __init tick_init(void); @@ -300,4 +301,10 @@ static inline void tick_nohz_task_switch(void) __tick_nohz_task_switch(); } +static inline void tick_nohz_user_enter_prepare(void) +{ + if (tick_nohz_full_cpu(smp_processor_id())) + rcu_nocb_flush_deferred_wakeup(); +} + #endif diff --git a/kernel/entry/common.c b/kernel/entry/common.c index a0b3b04fb596..bf16395b9e13 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -5,6 +5,7 @@ #include #include #include +#include #include "common.h" @@ -186,7 +187,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, local_irq_disable_exit_to_user(); /* Check if any of the above work has queued a deferred wakeup */ - rcu_nocb_flush_deferred_wakeup(); + tick_nohz_user_enter_prepare(); ti_work = READ_ONCE(current_thread_info()->flags); } @@ -202,7 +203,7 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs) lockdep_assert_irqs_disabled(); /* Flush pending rcuog wakeup before the last need_resched() check */ - rcu_nocb_flush_deferred_wakeup(); + tick_nohz_user_enter_prepare(); if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) ti_work = exit_to_user_mode_loop(regs, ti_work); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 828b091501ca..6784f27a3099 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -230,6 +230,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) #ifdef CONFIG_NO_HZ_FULL cpumask_var_t tick_nohz_full_mask; +EXPORT_SYMBOL_GPL(tick_nohz_full_mask); bool tick_nohz_full_running; EXPORT_SYMBOL_GPL(tick_nohz_full_running); static atomic_t tick_dep_mask; -- 2.25.1