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 3CEE0C5478C for ; Fri, 23 Feb 2024 12:42:29 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rdUs1-0007YC-7K; Fri, 23 Feb 2024 07:41:42 -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 1rdUpy-00075z-T4 for qemu-devel@nongnu.org; Fri, 23 Feb 2024 07:39:34 -0500 Received: from smtp-out2.suse.de ([2a07:de40:b251:101:10:150:64:2]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1rdUpq-00038e-UB for qemu-devel@nongnu.org; Fri, 23 Feb 2024 07:39:34 -0500 Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 19CEF1FBB5; Fri, 23 Feb 2024 12:39:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1708691965; h=from:from:reply-to: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=dK2rCsMw+TNlWZOeP8q1If5eK1wEPcLB+ZfWbg+Ez7w=; b=A0zRymI9PG3nsUhAYnDX7dmcqsxxvEv25HTaEBdb1CXuKDjEE2gaNnD23f01Xp0W58u7Xs jNFd7EKvJWfw1ToThKlBeFakW/wtJs+/Cfdw2an2CJ3J8LlDMO8pmGz0fZaLPfCBQdaDTn DT6oGMaAhZTLeRcmXG1CBEH4sVNSUgU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1708691965; h=from:from:reply-to: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=dK2rCsMw+TNlWZOeP8q1If5eK1wEPcLB+ZfWbg+Ez7w=; b=DimnQKCc1g8e0qypvGuVX7UOeZNpFA+edpnpgQzVGqmzCyDyd9B/VfydgJg8worWbkhX1o 9YxRxvUsal7TJtAg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1708691963; h=from:from:reply-to: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=dK2rCsMw+TNlWZOeP8q1If5eK1wEPcLB+ZfWbg+Ez7w=; b=JBWNEXiJHhpdDJMEcD69EJNYZ/gb1fNEgNLc4sG3thXuwhayrPlHP8MiJ6JnA+Mr8zBVX2 18uTuBthjGn4NDRDZhtoZ2ukVb4/2Ewn85PHkBfRFvNoXhW0Bw573eb6k4IWfOclhUe/TT X4BjO3ILumf++MRuhupxNahfeXlyec4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1708691963; h=from:from:reply-to: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=dK2rCsMw+TNlWZOeP8q1If5eK1wEPcLB+ZfWbg+Ez7w=; b=FjAhaZ2igQm+wORMCqIGk6peJ30jf0cCKUk9SfWv/RyLISiSMCg9tsWpjDCLBZhN9cqO+f F1K8LKCCTfmTIbBA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 95E5D133DC; Fri, 23 Feb 2024 12:39:22 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id VVKNF/qR2GXNdgAAD6G6ig (envelope-from ); Fri, 23 Feb 2024 12:39:22 +0000 From: Fabiano Rosas To: Peter Xu Cc: qemu-devel@nongnu.org Subject: Re: [PATCH] migration: Fix qmp_query_migrate mbps value In-Reply-To: References: <20240219194457.26923-1-farosas@suse.de> <87y1beascb.fsf@suse.de> <87ttm0a9t3.fsf@suse.de> Date: Fri, 23 Feb 2024 09:39:12 -0300 Message-ID: <87frxj9wy7.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Authentication-Results: smtp-out2.suse.de; none X-Spamd-Result: default: False [-3.10 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; BAYES_HAM(-3.00)[100.00%]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCPT_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[gitlab.com:url,suse.de:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[] Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:2; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Xu writes: > On Thu, Feb 22, 2024 at 10:49:12AM -0300, Fabiano Rosas wrote: >> Peter Xu writes: >> >> > On Thu, Feb 22, 2024 at 05:40:41PM +0800, Peter Xu wrote: >> >> On Wed, Feb 21, 2024 at 09:56:36AM -0300, Fabiano Rosas wrote: >> >> > Peter Xu writes: >> >> > >> >> > > On Mon, Feb 19, 2024 at 04:44:57PM -0300, Fabiano Rosas wrote: >> >> > >> The QMP command query_migrate might see incorrect throughput numbers >> >> > >> if it runs after we've set the migration completion status but before >> >> > >> migration_calculate_complete() has updated s->total_time and s->mbps. >> >> > >> >> >> > >> The migration status would show COMPLETED, but the throughput value >> >> > >> would be the one from the last iteration and not the one from the >> >> > >> whole migration. This will usually be a larger value due to the time >> >> > >> period being smaller (one iteration). >> >> > >> >> >> > >> Move migration_calculate_complete() earlier so that the status >> >> > >> MIGRATION_STATUS_COMPLETED is only emitted after the final counters >> >> > >> update. >> >> > >> >> >> > >> Signed-off-by: Fabiano Rosas >> >> > >> --- >> >> > >> CI run: https://gitlab.com/farosas/qemu/-/pipelines/1182405776 >> >> > >> --- >> >> > >> migration/migration.c | 10 ++++++---- >> >> > >> 1 file changed, 6 insertions(+), 4 deletions(-) >> >> > >> >> >> > >> diff --git a/migration/migration.c b/migration/migration.c >> >> > >> index ab21de2cad..7486d59da0 100644 >> >> > >> --- a/migration/migration.c >> >> > >> +++ b/migration/migration.c >> >> > >> @@ -102,6 +102,7 @@ static int migration_maybe_pause(MigrationState *s, >> >> > >> int new_state); >> >> > >> static void migrate_fd_cancel(MigrationState *s); >> >> > >> static bool close_return_path_on_source(MigrationState *s); >> >> > >> +static void migration_calculate_complete(MigrationState *s); >> >> > >> >> >> > >> static void migration_downtime_start(MigrationState *s) >> >> > >> { >> >> > >> @@ -2746,6 +2747,7 @@ static void migration_completion(MigrationState *s) >> >> > >> migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE, >> >> > >> MIGRATION_STATUS_COLO); >> >> > >> } else { >> >> > >> + migration_calculate_complete(s); >> >> > >> migrate_set_state(&s->state, current_active_state, >> >> > >> MIGRATION_STATUS_COMPLETED); >> >> > >> } >> >> > >> @@ -2784,6 +2786,7 @@ static void bg_migration_completion(MigrationState *s) >> >> > >> goto fail; >> >> > >> } >> >> > >> >> >> > >> + migration_calculate_complete(s); >> >> > >> migrate_set_state(&s->state, current_active_state, >> >> > >> MIGRATION_STATUS_COMPLETED); >> >> > >> return; >> >> > >> @@ -2993,12 +2996,15 @@ static void migration_calculate_complete(MigrationState *s) >> >> > >> int64_t end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); >> >> > >> int64_t transfer_time; >> >> > >> >> >> > >> + /* QMP could read from these concurrently */ >> >> > >> + bql_lock(); >> >> > >> migration_downtime_end(s); >> >> > >> s->total_time = end_time - s->start_time; >> >> > >> transfer_time = s->total_time - s->setup_time; >> >> > >> if (transfer_time) { >> >> > >> s->mbps = ((double) bytes * 8.0) / transfer_time / 1000; >> >> > >> } >> >> > >> + bql_unlock(); >> >> > > >> >> > > The lock is not needed? >> >> > > >> >> > > AFAIU that was needed because of things like runstate_set() rather than >> >> > > setting of these fields. >> >> > > >> >> > >> >> > Don't we need to keep the total_time and mbps update atomic? Otherwise >> >> > query-migrate might see (say) total_time=0 and mbps= or >> >> > total_time= and mbps=. >> >> >> >> I thought it wasn't a major concern, but what you said makes sense; taking >> >> it one more time doesn't really hurt after all to provide such benefit. >> >> >> >> > >> >> > Also, what orders s->mbps update before the s->state update? I'd say we >> >> > should probably hold the lock around the whole total_time,mbps,state >> >> > update. >> >> >> >> IMHO that's fine; mutex unlock implies a RELEASE. See atomic.rst: >> >> >> >> - ``pthread_mutex_lock`` has acquire semantics, ``pthread_mutex_unlock`` has >> >> release semantics and synchronizes with a ``pthread_mutex_lock`` for the >> >> same mutex. >> > >> > Hmm perhaps I wrote too soon.. it should only guarantee the ordering of the >> > update on the lock variable itself v.s. any previous R&Ws, nothing else. >> > Only if the other side uses bql_lock() will it guarantee proper ordering. >> > >> > Put them in bql should work, but I hesitate such use to start using bql >> > to protect state updates. >> >> Well, on the other hand that's a major use-case of the BQL: protecting >> state that's used by QMP. >> >> > >> > How about we drop the lock, but use an explicit smp_mb_release()? We may >> > also want to use smb_load_acquire() in fill_source_migration_info() to use >> > on reading &s->state (all will need some comment). To me, making sure the >> > total mbps is valid seems more important; while the other races are less >> > harmful, and may not be a major concern? >> >> That more closely reflects the problem we're trying to solve, which is >> just an ordering one. However, the QMP code already holds the BQL, we >> could just take benefit of that instead of adding more complex >> synchronization primitives. >> >> May I suggest we keep it simple and move that last migrate_set_state >> into the BQL as well? > > It's okay to me, but then let's also extend the comment a little bit on the > two exact requirements we're persuing (atomicity of updating fields, > ordering of state update v.s. mbps)? Ok, I'll respin with these changes. > > We can also rename migration_calculate_complete() to something like > migration_completion_finalize()? Then move the state update into it. I've been planning to merge migration_completion() and migration_iteration_finish(). It's too unintuitive to do the completion routine deep inside migration_iteration_run(). AFAICS those are all tail calls, so we could bring migration_completion() up into the migration_thread top level. So if you'll allow me I think I'll refrain from moving the state into migration_calculate_complete() for now.