From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-lf1-f43.google.com (mail-lf1-f43.google.com [209.85.167.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7CF221F583D; Thu, 12 Jun 2025 09:35:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.43 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749720921; cv=none; b=EW/2tnVNDNQS5pHSgazGuHdr3PLs2Bk8D1vHGfGH5hhsED4tPSxZruIAnQjMrgpn2pNhD6MXET5pAkO3DL6h3I/y382iqWnyG3SfMtxi+T6WEH0kL+73s/eM0nz8oiMky/gMbiwdZvxWl1e+1LV0A3HrEUsCYpknk6zs6pc6j+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749720921; c=relaxed/simple; bh=6FgB+WvGbctHgE61tfJuDhNLiJzdc+uwCPH8BFiCunc=; h=From:Date:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=tSiaMwkgFlpmjTkKMV4Xwh1tWIl+9sGBy/K8Tw1e1MIm5nGcMxeQ2Syw8HD4PYFwPA7ilnKXPPQVT21DqJU4LsdAo9GeHXrb3/yG+NANNmDJqHEpfbJq9udyVMJGPHJxb+ChhdwHYPWKxG2rmbIXT+jE845HunMdBohoo1Lr28Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=AFgHEJn5; arc=none smtp.client-ip=209.85.167.43 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="AFgHEJn5" Received: by mail-lf1-f43.google.com with SMTP id 2adb3069b0e04-55350d0eedeso640048e87.2; Thu, 12 Jun 2025 02:35:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1749720916; x=1750325716; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:from:to:cc:subject:date:message-id:reply-to; bh=B9XgOyLN+6u3eshF39lnx/D7xKZZthMQB0xJDbNgZRg=; b=AFgHEJn5lUKt9K0AzCuvo1Fd2ssPgwjk8b8D0yRmg63a4lupR7jJ9eEv2aaMHNcY9I GemvIaFKFn90zNITrCRF4+nv67fc0bm8Z2kttxk+lDptuXN/bAJoF4P28hYU/t4wwu7K 6I+FYQKyFR8hHmYy/gzW4C0mCAYJHONK6lPn1H9B/pSa68HdRSpQMy0QKvgD2flQHPun K7GfF8D5eriU4Kpe+mvAxL/7jCLL3No/3KgBzbN8ioSPIYoIzt5unbA3lZAiPdyeHFlr aWD7ZiNLrN1LGm5WD6G4IW2eXOkgqgmjjTgfXJ/wFuiOp8P7BCMti2lhi/q8Gp8tAJAw s/1w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1749720916; x=1750325716; 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 :message-id:reply-to; bh=B9XgOyLN+6u3eshF39lnx/D7xKZZthMQB0xJDbNgZRg=; b=LPrIyeQd5ur3PkbAZG4lFF0F6tzQV7t1/aUoA01TLTuHaaa/y0xl86KkwoJJTt8NWZ LhZMWxPhuOCiPwbSfmGO2PX1dvImG7yAHbXYXNZBYnHQ4VsIZCBz0S7XK86u/8s4BEhs 1hPzbcQqk8adi3OM4DrbaojvJNBFOq5VqKtSqrTuXrt5UY2EAfi9P8CeQR/6UET6sccz 6G8yUVDNFy/3Gw5vJRczd9mS3rZGaVoseTLul7o9RGmw/xe/Xt73crI9yK8q2woylzMl wXcTU0DSaz4jekp6KGfw0YCZnpBCvYvW+8u9n/3XTReJxCOPw+AiKJSCUbaGJV63iS2n hbdw== X-Forwarded-Encrypted: i=1; AJvYcCUx+kwgqCKY/OKFBLknv9oT8GAcLB/uftWsJNaD2jeAf2wzqOq2GBBPS7xvyi983+OVMS6x49XM3dRbDo8=@vger.kernel.org, AJvYcCWDRjOtrd3HWZS7Y5gxpgMIizCjr3SLXRZNbw3Hsk/cnEIypdRjtUha0iKHbqqYj5dd6b6Y@vger.kernel.org X-Gm-Message-State: AOJu0YzbXgcpYrP1oAhJGXmzfYxdVuWFJKrfyOyVFPjjEdj/s4rc4SyI Kh0h3frDO5++2lv1DKuTTmR4v/O+98VapOlTgnHDE0JXbxbOQsMoknis X-Gm-Gg: ASbGnctLjnQWtPvEu7vmMEetHYaDvP7FAz64bzh4EKXrU2LgTtxATYRuP3ivATME1rg IjfX5KsFrerc8mSf1kGxCAiNlHIdqw3ATSQCkrEepHo3yxDWeXTZZdzdMlhuhQ8+vGORBnpa2wn zMUJQUFxn911Nu3XgdDGdOo5sVA+JG/mg0TeSqDKi8XCT7MbKH1yFqoy8fNeWKx/PHGz2Fo8elv BUx53iZjsmqtzNfLeKQMKcEOajfJLWJmgwrHeXwok40wBVIU8PYnVYOBdzp1cQy55Ow4AR7chHQ DLn5SPwJwKNM4IDCt5qpyhydRmEJ4bzCK1eFEb3T16ex3I979Lx5+5vsm6N3R4PacdtOIhI4a9O ymggHz5jgIag= X-Google-Smtp-Source: AGHT+IHk9tDnmNn/N3vdm9Jt5yx4W3KvwzVpgTVmppRO7QaeWoYFfo3o/bOG1TFzmwYfFr7qISL+aA== X-Received: by 2002:a05:6512:3041:b0:553:35e6:3949 with SMTP id 2adb3069b0e04-553a55f4082mr778067e87.34.1749720916163; Thu, 12 Jun 2025 02:35:16 -0700 (PDT) Received: from pc636 (host-95-203-1-180.mobileonline.telia.com. [95.203.1.180]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-553ac13f0dbsm54594e87.85.2025.06.12.02.35.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Jun 2025 02:35:15 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 12 Jun 2025 11:35:12 +0200 To: Joel Fernandes Cc: "Uladzislau Rezki (Sony)" , "Paul E . McKenney" , Neeraj upadhyay , Joel Fernandes , RCU , LKML , Frederic Weisbecker Subject: Re: [PATCH v2 1/2] rcu: Enable rcu_normal_wake_from_gp on small systems Message-ID: References: <20250611175658.91361-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jun 11, 2025 at 05:48:57PM -0400, Joel Fernandes wrote: > > > On 6/11/2025 1:56 PM, Uladzislau Rezki (Sony) wrote: > > Automatically enable the rcu_normal_wake_from_gp parameter on > > systems with a small number of CPUs. The activation threshold > > is set to 16 CPUs. > > > > This helps to reduce a latency of normal synchronize_rcu() API > > by waking up GP-waiters earlier and decoupling synchronize_rcu() > > callers from regular callback handling. > > > > A benchmark running 64 parallel jobs(system with 64 CPUs) invoking > > synchronize_rcu() demonstrates a notable latency reduction with the > > setting enabled. > > Reviewed-by: Joel Fernandes > Thank you for review! > Just one nit below: > > > > > Latency distribution (microseconds): > > > > > > 0 - 9999 : 1 > > 10000 - 19999 : 4 > > 20000 - 29999 : 399 > > 30000 - 39999 : 3197 > > 40000 - 49999 : 10428 > > 50000 - 59999 : 17363 > > 60000 - 69999 : 15529 > > 70000 - 79999 : 9287 > > 80000 - 89999 : 4249 > > 90000 - 99999 : 1915 > > 100000 - 109999 : 922 > > 110000 - 119999 : 390 > > 120000 - 129999 : 187 > > ... > > > > > > > > 0 - 9999 : 1 > > 10000 - 19999 : 234 > > 20000 - 29999 : 6678 > > 30000 - 39999 : 33463 > > 40000 - 49999 : 20669 > > 50000 - 59999 : 2766 > > 60000 - 69999 : 183 > > ... > > > > > > Signed-off-by: Uladzislau Rezki (Sony) > > --- > > kernel/rcu/tree.c | 14 +++++++++++--- > > 1 file changed, 11 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index e8a4b720d7d2..b88ceb35cebd 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -1625,8 +1625,10 @@ static void rcu_sr_put_wait_head(struct llist_node *node) > > atomic_set_release(&sr_wn->inuse, 0); > > } > > > > -/* Disabled by default. */ > > -static int rcu_normal_wake_from_gp; > > +/* Enable rcu_normal_wake_from_gp automatically on small systems. */ > > +#define WAKE_FROM_GP_CPU_THRESHOLD 16 > > + > > +static int rcu_normal_wake_from_gp = -1; > > module_param(rcu_normal_wake_from_gp, int, 0644); > > static struct workqueue_struct *sync_wq; > > > > @@ -3239,7 +3241,7 @@ static void synchronize_rcu_normal(void) > > > > trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("request")); > > > > - if (!READ_ONCE(rcu_normal_wake_from_gp)) { > > + if (READ_ONCE(rcu_normal_wake_from_gp) < 1) { > > wait_rcu_gp(call_rcu_hurry); > > goto trace_complete_out; > > } > > @@ -4843,6 +4845,12 @@ void __init rcu_init(void) > > sync_wq = alloc_workqueue("sync_wq", WQ_MEM_RECLAIM, 0); > > WARN_ON(!sync_wq); > > > > + /* Respect if explicitly disabled via a boot parameter. */ > > + if (rcu_normal_wake_from_gp < 0) { > > + if (num_possible_cpus() <= WAKE_FROM_GP_CPU_THRESHOLD) > > + rcu_normal_wake_from_gp = 1; > > + } > > nit: better to just do: > > if (rcu_normal_wake_from_gp < 0 && > num_possible_cpus() <= WAKE_FROM_GP_CPU_THRESHOLD) > rcu_normal_wake_from_gp = 1; > } > Two lines anyway :) -- Uladzislau Rezki