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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29707C04A95 for ; Sun, 25 Sep 2022 08:57:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230404AbiIYI5U (ORCPT ); Sun, 25 Sep 2022 04:57:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229515AbiIYI5Q (ORCPT ); Sun, 25 Sep 2022 04:57:16 -0400 Received: from mail-ed1-x52b.google.com (mail-ed1-x52b.google.com [IPv6:2a00:1450:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83B6F27159; Sun, 25 Sep 2022 01:57:14 -0700 (PDT) Received: by mail-ed1-x52b.google.com with SMTP id a41so5349160edf.4; Sun, 25 Sep 2022 01:57:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:from:to:cc:subject:date; bh=jv1R7uybFiFnN62T7LeT8cPnORSx0H4iaSe0cVM3ZAc=; b=IoHiRSEI45ReK4Rc1Gp5BhLE9lC7AAdkThWNuB+KTHyY4Ao1xIoZ3Dm7trmnHBDK+f XOtjJDHGekOJgev+g5CR5mRc0WPjD78ipcL6/GVyX3dHrMLo+NkDe9p5+ShWXtC7JlUv d1+8iUh35Jt2d2IOU+qEtHkXvEJxRt3vQDM6spFjx43dUyolii29wtDP7pr280e15V3N T44w0r1lXVZTWIN519AIO31pPHEF6SKx2GesW+DRwVuQ7rPpVpW+Mz0gcvBenAROE5GR vx7ckQPlwu/Jb8pDDaSWPmD28KauI9rnkhUHFmhgA5rrzmQCYq0/J4GXjUvc2/MvJDRl ocAA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:x-gm-message-state:from:to:cc:subject:date; bh=jv1R7uybFiFnN62T7LeT8cPnORSx0H4iaSe0cVM3ZAc=; b=3NMeTcwHmxvEAOC6YAs+YrOZrBnlyz06YD/eqzWRLP+CZK0TWOkwB5dTCxeETeVbjK PhjUJ0ccQVj2lDZQOi2/mrHyPOpb060+dLysMBKhlxOXHlXGM9LqNuYGY+6W5S9k+Eyt N9T/Mmgcs8lxWb6bXB965LE3VH6j9jZtLy5tn9mQTTytoSsYXV5L0WZiATJX6i1TWGK/ mf+mIldh1zoQoonxoxslCPYSiaV4wSj+OfTIaDpLHxo32gQW9zHU8AcmNu5ICL/ICkHh BiENILFnh2DbFZOnBW9OqQPYnEMJ9qK4ATFayLmI06cKufgRiRSoRdVKldyAWrKWg6a2 1lvg== X-Gm-Message-State: ACrzQf0CtV4gk5g3Ljlmu/si/QfSyP0RpfvpgYqWOAePz6N6kHpogjER DpgP8YAOEpaE6rimHFjgzFVOShfqihKkDg== X-Google-Smtp-Source: AMsMyM4gzw+hC15lHyjSL1+1L1SU81RfqzHecb657gJouuBR3aC92MVix4qStEknLCVcsofj41Gmvw== X-Received: by 2002:aa7:d293:0:b0:457:65d:c0cb with SMTP id w19-20020aa7d293000000b00457065dc0cbmr5384303edq.25.1664096232886; Sun, 25 Sep 2022 01:57:12 -0700 (PDT) Received: from pc636 ([155.137.26.201]) by smtp.gmail.com with ESMTPSA id b2-20020aa7dc02000000b00457171d1fffsm1802052edu.44.2022.09.25.01.57.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Sep 2022 01:57:12 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Sun, 25 Sep 2022 10:57:10 +0200 To: "Joel Fernandes (Google)" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, rushikesh.s.kadam@intel.com, urezki@gmail.com, neeraj.iitr10@gmail.com, frederic@kernel.org, paulmck@kernel.org, rostedt@goodmis.org Subject: Re: [PATCH v6 1/4] rcu: Make call_rcu() lazy to save power Message-ID: References: <20220922220104.2446868-1-joel@joelfernandes.org> <20220922220104.2446868-2-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220922220104.2446868-2-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Implement timer-based RCU lazy callback batching. The batch is flushed > whenever a certain amount of time has passed, or the batch on a > particular CPU grows too big. Also memory pressure will flush it in a > future patch. > > To handle several corner cases automagically (such as rcu_barrier() and > hotplug), we re-use bypass lists to handle lazy CBs. The bypass list > length has the lazy CB length included in it. A separate lazy CB length > counter is also introduced to keep track of the number of lazy CBs. > > v5->v6: > > [ Frederic Weisbec: Program the lazy timer only if WAKE_NOT, since other > deferral levels wake much earlier so for those it is not needed. ] > > [ Frederic Weisbec: Use flush flags to keep bypass API code clean. ] > > [ Frederic Weisbec: Make rcu_barrier() wake up only if main list empty. ] > > [ Frederic Weisbec: Remove extra 'else if' branch in rcu_nocb_try_bypass(). ] > > [ Joel: Fix issue where I was not resetting lazy_len after moving it to rdp ] > > [ Paul/Thomas/Joel: Make call_rcu() default lazy so users don't mess up. ] > I think it make sense to add some data to the commit message illustrating what this patch does. >From my side i gave a try of this patch on my setup. Some data: root@pc638:/home/urezki/rcu_v6# ./perf_script_parser ./perf_v6.script | sort -nk 6 | grep rcu name: rcuop/23 pid: 184 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/26 pid: 206 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/29 pid: 227 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/2 pid: 35 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/33 pid: 256 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/34 pid: 263 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/35 pid: 270 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/36 pid: 277 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/37 pid: 284 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/38 pid: 291 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/49 pid: 370 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/59 pid: 441 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/63 pid: 469 woken-up 1 interval: min 0 max 0 avg 0 name: rcuog/0 pid: 16 woken-up 2 interval: min 8034 max 8034 avg 4017 name: rcuog/24 pid: 191 woken-up 2 interval: min 7941 max 7941 avg 3970 name: rcuog/32 pid: 248 woken-up 2 interval: min 7542 max 7542 avg 3771 name: rcuog/48 pid: 362 woken-up 2 interval: min 8065 max 8065 avg 4032 name: rcuog/56 pid: 419 woken-up 2 interval: min 8076 max 8076 avg 4038 name: rcuop/21 pid: 170 woken-up 2 interval: min 13311438 max 13311438 avg 6655719 name: rcuog/16 pid: 134 woken-up 4 interval: min 8029 max 13303387 avg 3329863 name: rcuop/9 pid: 85 woken-up 4 interval: min 10007570 max 10007586 avg 7505684 name: rcuog/8 pid: 77 woken-up 8 interval: min 6240 max 10001242 avg 3753622 name: rcu_preempt pid: 15 woken-up 18 interval: min 6058 max 9999713 avg 2140788 name: test_rcu/0 pid: 1411 woken-up 10003 interval: min 165 max 19072 avg 4275 root@pc638:/home/urezki/rcu_v6# root@pc638:/home/urezki/rcu_v6# ./perf_script_parser ./perf_default.script | sort -nk 6 | grep rcu name: rcuop/33 pid: 256 woken-up 1 interval: min 0 max 0 avg 0 name: rcuop/51 pid: 384 woken-up 1 interval: min 0 max 0 avg 0 name: rcuog/32 pid: 248 woken-up 2 interval: min 11927 max 11927 avg 5963 name: rcuop/63 pid: 469 woken-up 2 interval: min 23963 max 23963 avg 11981 name: rcuog/56 pid: 419 woken-up 3 interval: min 11132 max 23967 avg 11699 name: rcuop/50 pid: 377 woken-up 3 interval: min 8057 max 4944344 avg 1650800 name: rcuog/48 pid: 362 woken-up 8 interval: min 2712 max 37430015 avg 5298801 name: rcuop/16 pid: 135 woken-up 4790 interval: min 7340 max 16649 avg 8843 name: rcuog/16 pid: 134 woken-up 4792 interval: min 7368 max 16644 avg 8844 name: rcu_preempt pid: 15 woken-up 5302 interval: min 26 max 12179 avg 7994 name: test_rcu/0 pid: 1353 woken-up 10003 interval: min 169 max 18508 avg 4236 root@pc638:/home/urezki/rcu_v6# so it is obvious that the patch does the job. On my KVM machine the boot time is affected: [ 2.273406] e1000 0000:00:03.0 eth0: Intel(R) PRO/1000 Network Connection [ 11.945283] e1000 0000:00:03.0 ens3: renamed from eth0 [ 22.165198] sr 1:0:0:0: [sr0] scsi3-mmc drive: 4x/4x cd/rw xa/form2 tray [ 22.165206] cdrom: Uniform CD-ROM driver Revision: 3.20 [ 32.406981] sr 1:0:0:0: Attached scsi CD-ROM sr0 [ 104.115418] process '/usr/bin/fstype' started with executable stack [ 104.170142] EXT4-fs (sda1): mounted filesystem with ordered data mode. Quota mode: none. [ 104.340125] systemd[1]: systemd 241 running in system mode. (+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid) [ 104.340193] systemd[1]: Detected virtualization kvm. [ 104.340196] systemd[1]: Detected architecture x86-64. [ 104.359032] systemd[1]: Set hostname to . [ 105.740109] random: crng init done [ 105.741267] systemd[1]: Reached target Remote File Systems. 2 - 11 and second delay is between 32 - 104. So there are still users which must be waiting for "RCU" in a sync way. > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 08605ce7379d..40ae36904825 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -108,6 +108,13 @@ static inline int rcu_preempt_depth(void) > > #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ > > +#ifdef CONFIG_RCU_LAZY > +void call_rcu_flush(struct rcu_head *head, rcu_callback_t func); > +#else > +static inline void call_rcu_flush(struct rcu_head *head, > + rcu_callback_t func) { call_rcu(head, func); } > +#endif > + > /* Internal to kernel */ > void rcu_init(void); > extern int rcu_scheduler_active; > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > index f53ad63b2bc6..edd632e68497 100644 > --- a/kernel/rcu/Kconfig > +++ b/kernel/rcu/Kconfig > @@ -314,4 +314,12 @@ config TASKS_TRACE_RCU_READ_MB > Say N here if you hate read-side memory barriers. > Take the default if you are unsure. > > +config RCU_LAZY > + bool "RCU callback lazy invocation functionality" > + depends on RCU_NOCB_CPU > + default n > + help > + To save power, batch RCU callbacks and flush after delay, memory > + pressure or callback list growing too big. > + > Do you think you need this kernel option? Can we just consider and make it a run-time configurable? For example much more users will give it a try, so it will increase a coverage. By default it can be off. Also you do not need to do: #ifdef LAZY ... #else ... #endif > > +/* > + * LAZY_FLUSH_JIFFIES decides the maximum amount of time that > + * can elapse before lazy callbacks are flushed. Lazy callbacks > + * could be flushed much earlier for a number of other reasons > + * however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are > + * left unsubmitted to RCU after those many jiffies. > + */ > +#define LAZY_FLUSH_JIFFIES (10 * HZ) > +static unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES; Make it configurable? I do not think you actually need 10 seconds here. Reducing it will reduce a possibility to hit a low memory condition. 1 second would be far enough i think. -- Uladzislau Rezki