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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 55DF0C282C4 for ; Tue, 12 Feb 2019 15:24:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1545020863 for ; Tue, 12 Feb 2019 15:24:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b="be4ovrtR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729994AbfBLPYN (ORCPT ); Tue, 12 Feb 2019 10:24:13 -0500 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:33934 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727248AbfBLPYM (ORCPT ); Tue, 12 Feb 2019 10:24:12 -0500 Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id 457DE8EE1A4; Tue, 12 Feb 2019 07:24:12 -0800 (PST) Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id BB-nU0NLE4nO; Tue, 12 Feb 2019 07:24:12 -0800 (PST) Received: from [153.66.254.194] (unknown [50.35.68.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id 8C9CF8EE0E9; Tue, 12 Feb 2019 07:24:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1549985051; bh=aMg0DSQ4n/Oa8YY0OlX8mifTi163h3Bndg4yTi/z6Tk=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=be4ovrtRhytJQRNLZfvQPLyez4/TQjFDRQ/hzMI/wetdnkVfnHpQisZouLO/26J0V rZt54HVJXf9+n6Osv5uAEBWiACdtaCjXR9//SYaIfEG+OoCD/2tMc4If+yTY50ZkUw 0XsGJj0Bavpjtbu4MnnXjCu/OA5pzUH2RxI19lRE= Message-ID: <1549985049.3173.3.camel@HansenPartnership.com> Subject: Re: [5.0-rc5 regression] "scsi: kill off the legacy IO path" causes 5 minute delay during boot on Sun Blade 2500 From: James Bottomley To: Jens Axboe , Mikael Pettersson , Xuewei Zhang Cc: Linux SPARC Kernel Mailing List , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi Date: Tue, 12 Feb 2019 07:24:09 -0800 In-Reply-To: References: <1549736341.2971.7.camel@HansenPartnership.com> <1549813472.4142.3.camel@HansenPartnership.com> <3380ed8e-ae02-96f2-142b-7cce09459df8@kernel.dk> <1549815924.4142.8.camel@HansenPartnership.com> <0e6e5d67-d305-dd00-2e42-e2299166c8b2@kernel.dk> <1549898730.2831.6.camel@HansenPartnership.com> <44bb4374-0b7c-733b-a53e-92d2f03f2f49@kernel.dk> <1549899773.2831.12.camel@HansenPartnership.com> <1a00da0e-cb8e-30ea-8d17-120f97242b2f@kernel.dk> <1549902521.2831.23.camel@HansenPartnership.com> <1549937598.2857.8.camel@HansenPartnership.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-02-11 at 19:50 -0700, Jens Axboe wrote: > On 2/11/19 7:13 PM, James Bottomley wrote: > > On Mon, 2019-02-11 at 09:31 -0700, Jens Axboe wrote: > > > On 2/11/19 9:28 AM, James Bottomley wrote: > > > > On Mon, 2019-02-11 at 08:46 -0700, Jens Axboe wrote: > > > > > On 2/11/19 8:42 AM, James Bottomley wrote: > > > > > > On Mon, 2019-02-11 at 08:28 -0700, Jens Axboe wrote: > > > > > > > On 2/11/19 8:25 AM, James Bottomley wrote: > > > > > > > > On Sun, 2019-02-10 at 09:35 -0700, Jens Axboe wrote: > > > > > > > > > On 2/10/19 9:25 AM, James Bottomley wrote: > > > > > > > > [...] > > > > > > > > > > That check wasn't changed by the code removal. > > > > > > > > > > > > > > > > > > As I said above, for sd. This isn't true for non- > > > > > > > > > disks. > > > > > > > > > > > > > > > > Yes, but the behaviour above doesn't change across a > > > > > > > > switch > > > > > > > > to MQ, so I don't quite understand how it bisects back > > > > > > > > to > > > > > > > > that change. If we're not gathering entropy for the > > > > > > > > device > > > > > > > > now, we wouldn't have been before the switch, so the > > > > > > > > entropy characteristics shouldn't have changed. > > > > > > > > > > > > > > But it does, as I also wrote in that first email. The > > > > > > > legacy > > > > > > > queue flags had QUEUE_FLAG_ADD_RANDOM set by default, the > > > > > > > MQ > > > > > > > ones do not. Hence any non-sd device would previously > > > > > > > ALWAYS > > > > > > > have ADD_RANDOM set, now none of them do. Also see the > > > > > > > patch > > > > > > > I sent. > > > > > > > > > > > > So your theory is that the disk in question never gets to > > > > > > the > > > > > > rotational check? because the check will clear the flag if > > > > > > it's non-rotational and set it if it's not, so the default > > > > > > state of the flag shouldn't matter. > > > > > > > > > > No, my point is about non-disks, devices that aren't driven > > > > > by > > > > > sd. The behavior for sd hasn't changed, as it sets/clears it > > > > > unconditionally. > > > > > > > > I agree, but I don't think any of them were significant entropy > > > > contributors before: things like nvme have always been outside > > > > of > > > > this and sr and st don't really contribute much to the seek > > > > load > > > > during boot because they're probed but not used by the boot > > > > sequence, so I can't see how they would cause this > > > > behaviour. I > > > > suppose it could be target probing, but even that seems > > > > unlikely > > > > because it should be dwarfed by the number of root disk reads > > > > during boot. > > > > > > > > For the rng to take an additional 5 minutes to initialize, we > > > > must > > > > have lost a significant entropy source somewhere. > > > > > > I agree it's not a significant amount of entropy, but even just > > > one > > > bit could mean a long stall if that put us over the edge of just > > > not > > > having enough for whatever is blocking on /dev/random. Mikael's > > > boot > > > did have a CDROM, it's not impossible that the handful of > > > commands we > > > end up doing to that device would have contributed enough entropy > > > to > > > get the boot done without stalling for minutes. > > > > > > One way to know for sure, and that's if Mikael tests the patch. > > > > I think I've got the root cause. I have one system in my test bed > > exhibiting this behaviour. It turns out the disk in it has no > > characteristics VPD page. The 0xB1 VPD was a SBC-3 addition, so > > that's > > not surprising. However, the characteristics check bails before > > setting the flags, so it takes the default flag which has flipped. > > > > We can either fix this by setting the QUEUE_FLAG_ADD_RANDOM if > > there's > > no 0xB1 page or by setting the default as Jens proposed. > > I'd recommend just doing my patch, since that'll be the same behavior > that SCSI had before. I've got the history now, it's this patch Author: Xuewei Zhang Date: Thu Sep 6 13:37:19 2018 -0700 scsi: sd: Contribute to randomness when running rotational device It added the else branch to the if (rot == 1). It's the position of that else branch which is wrong because not all disks have a SBC-3 characteristics VPD page, so they're the ones under MQ which stop contributing entropy. Whichever patch we go with will need a fixes: for this. James