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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 D2092C2D0CE for ; Tue, 21 Jan 2020 14:19:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9CC352087E for ; Tue, 21 Jan 2020 14:19:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579616364; bh=es0Pkse8eWBu3dyEGSJg1DKtzsKELcYDoDjvA1HrvEQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=eWTKHv3J/gkXFa61C/jrLCRW2Z0nf/WDGkLZeBmJiSOaZfJUbIC0LYzQgANXafFm+ lFFeAz5O71O1dOYEzfeTkWKiBHHan5wzUFEtykcGWwpXiRbvqKraT0/4zIUiSvjOcO rsd+MwXDyeGQ53Gd5yWp+l+lHECaFP8YnKVj+1ts= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728916AbgAUOTY (ORCPT ); Tue, 21 Jan 2020 09:19:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:44980 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727508AbgAUOTY (ORCPT ); Tue, 21 Jan 2020 09:19:24 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 763F02087E; Tue, 21 Jan 2020 14:19:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579616363; bh=es0Pkse8eWBu3dyEGSJg1DKtzsKELcYDoDjvA1HrvEQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=nbjIT4sZsmS+T8V62ilhv/+lAGTFFopFhVNCnDbCqRyXhl4WNu4tJIn2XIyM2wdsa nNm5l+Q/SBYhrKGlAIfTAQ1sJqrMWta73pJNkZEAnyJu08JaAbrzuOUiaBS4Jv1zct 2CGK4vUS6EAaH7OlP9WeVdJorUdx35Zn7/WlWuKc= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4A76035227E4; Tue, 21 Jan 2020 06:19:23 -0800 (PST) Date: Tue, 21 Jan 2020 06:19:23 -0800 From: "Paul E. McKenney" To: Qian Cai Cc: rcu@vger.kernel.org, LKML Subject: Re: Boot warning at rcu_check_gp_start_stall() Message-ID: <20200121141923.GP2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200121050941.GO2935@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Tue, Jan 21, 2020 at 06:45:32AM -0500, Qian Cai wrote: > > > > On Jan 21, 2020, at 12:09 AM, Paul E. McKenney wrote: > > > > This is what you get when a grace period has been requested, but does > > not start within 21 seconds or so. The "->state: 0x1ffff" is a new one > > on me -- that normally happens only before RCU's grace-period kthread > > has been spawned. But by 97 seconds after boot, it should definitely > > already be up and running. > > > > Is the system responsive at this point? > > Yes, it works fine. > > > Except... Why is it taking 96 seconds for the system to get to the point > > where it prints "Dentry cache hash table entries:"? That happens at 0.139 > > seconds on my laptop. And at about the same time on a much larger system. > > > > I could easily imagine that all sorts of things would break when boot > > takes that long. > > I suppose the kernel has CONFIG_EFI_PGT_DUMP=y, so it takes a while to run just before rcu_check_gp_start_stall(). New one on me! One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300, which would allow more time. Longer term, I could suppress this warning during boot when CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific. Alternatively, I could provide a Kconfig option that suppressed this during boot that was selected by whatever long-running boot-time Kconfig option needed it. Yet another approach would be for long-running operations like efi_dump_pagetable() to suppress stalls on entry and re-enable them upon exit. Thoughts? Thanx, Paul