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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 643AAE67A8A for ; Wed, 4 Mar 2026 12:41:14 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vxlWq-0005s1-AE; Wed, 04 Mar 2026 07:40:40 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vxlWh-0005q1-7F for qemu-devel@nongnu.org; Wed, 04 Mar 2026 07:40:31 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vxlWe-0004ZJ-G0 for qemu-devel@nongnu.org; Wed, 04 Mar 2026 07:40:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772628026; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=wXgpZHmqrmykMYuioUb5WDstfmLdu4Eg9IrCF/WQyX0=; b=Q7qmsT+g3/kyAeFHvHiyUxP2BCMKKzyhCW7aRlKgqFqgxuILDmg/fxLbldQVNju0hE29Gm T6pwpgb8UwIrcZC2hMe7I9weqwnsnblgrWS5ZHCZ/puVz0MWoeSuPZ5lbxuRZ2QJ5TXmbH sfuV/TSYDrvo/QXawHRiosQP+FOsVWI= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-259-dKSiDhGSPM2YeadbRneASw-1; Wed, 04 Mar 2026 07:40:23 -0500 X-MC-Unique: dKSiDhGSPM2YeadbRneASw-1 X-Mimecast-MFC-AGG-ID: dKSiDhGSPM2YeadbRneASw_1772628021 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9B5A618005B4; Wed, 4 Mar 2026 12:40:21 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.75]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 28170195608E; Wed, 4 Mar 2026 12:40:17 +0000 (UTC) Date: Wed, 4 Mar 2026 12:40:14 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Kevin Wolf Cc: qemu-block@nongnu.org, hreitz@redhat.com, xeor@yandex-team.ru, vsementsov@yandex-team.ru, pkrempa@redhat.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org Subject: Re: [PATCH v2] block: Never drop BLOCK_IO_ERROR with action=stop for rate limiting Message-ID: References: <20260304122800.51923-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260304122800.51923-1-kwolf@redhat.com> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 0 X-Spam_score: -0.0 X-Spam_bar: / X-Spam_report: (-0.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.703, RCVD_IN_VALIDITY_SAFE_BLOCKED=1.386, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Mar 04, 2026 at 01:28:00PM +0100, Kevin Wolf wrote: > Commit 2155d2dd introduced rate limiting for BLOCK_IO_ERROR to emit an > event only once a second. This makes sense for cases in which the guest > keeps running and can submit more requests that would possibly also fail > because there is a problem with the backend. > > However, if the error policy is configured so that the VM is stopped on > errors, this is both unnecessary because stopping the VM means that the > guest can't issue more requests and in fact harmful because stopping the > VM is an important state change that management tools need to keep track > of even if it happens more than once in a given second. If an event is > dropped, the management tool would see a VM randomly going to paused > state without an associated error, so it has a hard time deciding how to > handle the situation. > > This patch disables rate limiting for action=stop by not relying on the > event type alone any more in monitor_qapi_event_queue_no_reenter(), but > checking action for BLOCK_IO_ERROR, too. If the error is reported to the > guest or ignored, the rate limiting stays in place. > > Fixes: 2155d2dd7f73 ('block-backend: per-device throttling of BLOCK_IO_ERROR reports') > Signed-off-by: Kevin Wolf > --- > qapi/block-core.json | 2 +- > monitor/monitor.c | 21 ++++++++++++++++++++- > 2 files changed, 21 insertions(+), 2 deletions(-) > > diff --git a/qapi/block-core.json b/qapi/block-core.json > index b66bf316e2f..da0b36a3751 100644 > --- a/qapi/block-core.json > +++ b/qapi/block-core.json > @@ -5794,7 +5794,7 @@ > # .. note:: If action is "stop", a `STOP` event will eventually follow > # the `BLOCK_IO_ERROR` event. > # > -# .. note:: This event is rate-limited. > +# .. note:: This event is rate-limited, except if action is "stop". > # > # Since: 0.13 > # > diff --git a/monitor/monitor.c b/monitor/monitor.c > index 1273eb72605..37fa674cfe6 100644 > --- a/monitor/monitor.c > +++ b/monitor/monitor.c > @@ -367,14 +367,33 @@ monitor_qapi_event_queue_no_reenter(QAPIEvent event, QDict *qdict) > { > MonitorQAPIEventConf *evconf; > MonitorQAPIEventState *evstate; > + bool throttled; > > assert(event < QAPI_EVENT__MAX); > evconf = &monitor_qapi_event_conf[event]; > trace_monitor_protocol_event_queue(event, qdict, evconf->rate); > + throttled = evconf->rate; > + > + /* > + * Rate limit BLOCK_IO_ERROR only for action != "stop". > + * > + * If the VM is stopped after an I/O error, this is important information > + * for the management tool to keep track of the state of QEMU and we can't > + * merge any events. At the same time, stopping the VM means that the guest > + * can't send additional requests and the number of events is already > + * limited, so we can do without rate limiting. > + */ > + if (event == QAPI_EVENT_BLOCK_IO_ERROR) { > + QDict *data = qobject_to(QDict, qdict_get(qdict, "data")); > + const char *action = qdict_get_str(data, "action"); > + if (!strcmp(action, "stop")) { > + throttled = false; > + } > + } Can this be handled in the same way as other events viat he qapi_event_throttle_hash & qapi_event_throttle_equal methods ? eg if action is "stop", then ensure "equal" is always false ? Possibly add a random token to the hash but might not be needed if 'equal' is always false > > QEMU_LOCK_GUARD(&monitor_lock); > > - if (!evconf->rate) { > + if (!throttled) { > /* Unthrottled event */ > monitor_qapi_event_emit(event, qdict); > } else { > -- > 2.53.0 > > With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|