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 7AE3AC433EF for ; Thu, 30 Jun 2022 09:29:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232911AbiF3J3A (ORCPT ); Thu, 30 Jun 2022 05:29:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33290 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230029AbiF3J26 (ORCPT ); Thu, 30 Jun 2022 05:28:58 -0400 Received: from alexa-out-sd-02.qualcomm.com (alexa-out-sd-02.qualcomm.com [199.106.114.39]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2723A112 for ; Thu, 30 Jun 2022 02:28:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1656581338; x=1688117338; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=0DTG2u6m3ZJQ1eowa1Tp9B3y0nN+bfBmbgViftnv1Aw=; b=wmLZTUIjbmIGUYpqZesy0HS3bxOKc2Z+g/hYAiD8tM1eMTXB+SRU+2kv ZAZSyXj5rIScRJuPCfQc2XwLBOQVUDuQweDPn20/KXqJRXfoVpD5fIpXT y07KNbMYWD8MP05OuWpI/d11pENCHx9MFiqvVA6STFspv1Gc4CVSEJzxr 0=; Received: from unknown (HELO ironmsg01-sd.qualcomm.com) ([10.53.140.141]) by alexa-out-sd-02.qualcomm.com with ESMTP; 30 Jun 2022 02:28:57 -0700 X-QCInternal: smtphost Received: from nasanex01b.na.qualcomm.com ([10.46.141.250]) by ironmsg01-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Jun 2022 02:28:57 -0700 Received: from [10.50.30.42] (10.80.80.8) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Thu, 30 Jun 2022 02:28:52 -0700 Message-ID: <95d8e5c0-e382-4e8a-c8c6-2acbc0d31ca8@quicinc.com> Date: Thu, 30 Jun 2022 14:58:49 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH v2] srcu: Reduce blocking agressiveness of expedited grace periods further Content-Language: en-US To: Marc Zyngier CC: , , , , , , , , , , , , , , , References: <20220630041201.18301-1-quic_neeraju@quicinc.com> <87o7ya1ozz.wl-maz@kernel.org> From: Neeraj Upadhyay In-Reply-To: <87o7ya1ozz.wl-maz@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nasanex01b.na.qualcomm.com (10.46.141.250) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/30/2022 2:56 PM, Marc Zyngier wrote: > On Thu, 30 Jun 2022 05:12:01 +0100, > Neeraj Upadhyay wrote: >> >> Commit 640a7d37c3f4 ("srcu: Block less aggressively for expedited >> grace periods") highlights a problem where aggressively blocking >> SRCU expedited grace periods, as was introduced in commit >> 282d8998e997 ("srcu: Prevent expedited GPs and blocking readers >> from consuming CPU"), introduces ~2 minutes delay to the overall >> ~3.5 minutes boot time, when starting VMs with "-bios QEMU_EFI.fd" >> cmdline on qemu, which results in very high rate of memslots >> add/remove, which causes > ~6000 synchronize_srcu() calls for >> kvm->srcu SRCU instance. >> >> Below table captures the experiments done by Zhangfei Gao and Shameer >> to measure the boottime impact with various values of non-sleeping >> per phase counts, with HZ_250 and preemption enabled: >> >> +──────────────────────────+────────────────+ >> | SRCU_MAX_NODELAY_PHASE | Boot time (s) | >> +──────────────────────────+────────────────+ >> | 100 | 30.053 | >> | 150 | 25.151 | >> | 200 | 20.704 | >> | 250 | 15.748 | >> | 500 | 11.401 | >> | 1000 | 11.443 | >> | 10000 | 11.258 | >> | 1000000 | 11.154 | >> +──────────────────────────+────────────────+ >> >> Analysis on the experiment results showed improved boot time >> with non blocking delays close to one jiffy duration. This >> was also seen when number of per-phase iterations were scaled >> to one jiffy. >> >> So, this change scales per-grace-period phase number of non-sleeping >> polls, such that, non-sleeping polls are done for one jiffy. In addition >> to this, srcu_get_delay() call in srcu_gp_end(), which is used to calculate >> the delay used for scheduling callbacks, is replaced with the check for >> expedited grace period. This is done, to schedule cbs for completed expedited >> grace periods immediately, which results in improved boot time seen in >> experiments. >> >> In addition to the changes to default per phase delays, this change >> adds 3 new kernel parameters - srcutree.srcu_max_nodelay, >> srcutree.srcu_max_nodelay_phase, srcutree.srcu_retry_check_delay. >> This allows users to configure the srcu grace period scanning delays, >> depending on their system configuration requirements. >> >> Signed-off-by: Neeraj Upadhyay >> Tested-by: Marc Zyngier >> --- >> >> Change in v2: >> >> - Change srcu_max_nodelay default value to consider phase delay >> iterations >> - Apply Pauls' feedback >> - Add Marc's Tested-by > > I gave this a go on the same platform as v1, and the result is > actually much better as I didn't have to add any extra command-line > option to get to a reasonable result (41s). I think we have a winner. > Thank you for testing it! Thanks Neeraj > Thanks again, > > M. >