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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 E4BE4C433DB for ; Tue, 9 Feb 2021 17:28:41 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5CA8564DF2 for ; Tue, 9 Feb 2021 17:28:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5CA8564DF2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42742 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9Woa-0000Z0-7a for qemu-devel@archiver.kernel.org; Tue, 09 Feb 2021 12:28:40 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:53062) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9WkM-0006Ky-3o for qemu-devel@nongnu.org; Tue, 09 Feb 2021 12:24:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:21108) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9WkD-0004fP-IP for qemu-devel@nongnu.org; Tue, 09 Feb 2021 12:24:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612891448; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eSi/D0ji/5Fh01NENW+fjxr0I+W0dCdSAvldvY7BxYo=; b=N+v3EyR2gRczPw3Rn8IiEDwCt+fOWH6ZcDi2Afm68eSbSaam/W2+Vc+Wtr0P2qWhlwYcny qR1083VGleb2w+J2T/WCPF0Ybmmn6Keyy7Ra9luRR3cvxbcN6JxNYHzU2e+tIUv5PldROI egTCnMDAKrumJBODGqd1laXkHjPzqMI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-15-WKY3rPBWNhKSt4WyT7A8cw-1; Tue, 09 Feb 2021 12:24:06 -0500 X-MC-Unique: WKY3rPBWNhKSt4WyT7A8cw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D8DF6BBEE4; Tue, 9 Feb 2021 17:24:04 +0000 (UTC) Received: from gondolin (ovpn-112-148.ams2.redhat.com [10.36.112.148]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9FECE60C61; Tue, 9 Feb 2021 17:24:03 +0000 (UTC) Date: Tue, 9 Feb 2021 18:24:00 +0100 From: Cornelia Huck To: Peter Maydell Subject: Re: getting the console output for s390 cdrom-test? Message-ID: <20210209182400.4fe15232.cohuck@redhat.com> In-Reply-To: References: <5213f033-19dc-bc40-bfd7-10b8c676539b@redhat.com> <20210209181009.7f2cb328.cohuck@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=cohuck@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.57, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, T_SPF_TEMPERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eric Farman , Thomas Huth , QEMU Developers , qemu-s390x Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 9 Feb 2021 17:17:19 +0000 Peter Maydell wrote: > On Tue, 9 Feb 2021 at 17:10, Cornelia Huck wrote: > > > > On Tue, 9 Feb 2021 14:58:53 +0000 > > Peter Maydell wrote: > > > This change significantly reduces the frequency with which I see > > > the hang; but it doesn't get rid of it altogether. Also I couldn't > > > really figure out from the virtio spec exactly where barriers > > > were required: I think I would need to read the whole thing in > > > more detail rather than trying to fish out the information by > > > just reading small pieces of it. > > > > The Linux virtio-ccw code uses 'weak barriers', i.e. the heavy bcr15 > > should not be needed. We might well miss other (lightweight) barriers > > in other parts of the code part, though. > > Is that the version the Linux kernel has as > /* Fast-BCR without checkpoint synchronization */ > #define __ASM_BARRIER "bcr 14,0\n" > > ? No, just a simple memory barrier in most places (bcr15 and bcr14 do serialization). > > > > But some of the ordering of > > > operations the spec describes doesn't match how the s390-ccw > > > BIOS code is doing it at all (eg the spec says that when feeding > > > a batch of descriptors to the device the driver isn't supposed to > > > update the flags on the first descriptor until it's finished > > > writing all of the descriptors, but the code doesn't seem to > > > try to do that). So I think the code could use an overhaul from > > > somebody with a better understanding of virtio than me... > > > > Yeah, the bios virtio code could probably use some love. > > > > I'm wondering how much memory ordering on the host platform influences > > things. I doubt many people try to run an s390x guest on an aarch64 > > host... > > Yes, you won't see this bug unless you're running QEMU on a > host that's pretty enthusiastic about reordering memory > transactions (and you'd never have seen it at all back when > we ran the iothread actions synchronously with the emulated > CPU, which we probably did back in 2013 when the s390-ccw > virtio code was written...) I haven't tested other aarch64 > hosts but I would be unsurprised to find that whether you > could repro it and how frequently depended on the particular > h/w implementation. I guess that hardly any s390x guests run on hw that's not either s390x or x86...