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 A1094C3601A for ; Thu, 3 Apr 2025 13:07:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u0KHr-0001N0-Ed; Thu, 03 Apr 2025 09:07:15 -0400 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 1u0KHp-0001Mh-IG for qemu-devel@nongnu.org; Thu, 03 Apr 2025 09:07:13 -0400 Received: from smtp-out1.suse.de ([195.135.223.130]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1u0KHn-0005T4-Ks for qemu-devel@nongnu.org; Thu, 03 Apr 2025 09:07:13 -0400 Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (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-out1.suse.de (Postfix) with ESMTPS id 5B9E721180; Thu, 3 Apr 2025 13:07:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1743685629; 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=1iuQSaorUWabAgc6jDeLPIp1/uUYmPqoK+E2pdwgDEo=; b=vsuq3rvM6cAEihUHjdqCQnfDUzRZOqKCL3nFXFLF2b4OoNgUcY1wekFeDn+CW0V9V64tB0 HVnb3bUb0G1yU4WfbZB23uxspllMkcqAVkEXZpAxWoZa6pO7Ka3TjurxXArY++HVcEvaBu ZjuiFYJon7KWswRDIoM1BxRcHXNWA7M= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1743685629; 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=1iuQSaorUWabAgc6jDeLPIp1/uUYmPqoK+E2pdwgDEo=; b=207CdiegPooCFCMoIgPpQyyIqXPAYf3ImTlQrUkgNwJyYAEtArQEritCvftbqkzkA4E7q+ mC5OpFOvxb8SiHDg== Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=vsuq3rvM; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=207Cdieg DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1743685629; 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=1iuQSaorUWabAgc6jDeLPIp1/uUYmPqoK+E2pdwgDEo=; b=vsuq3rvM6cAEihUHjdqCQnfDUzRZOqKCL3nFXFLF2b4OoNgUcY1wekFeDn+CW0V9V64tB0 HVnb3bUb0G1yU4WfbZB23uxspllMkcqAVkEXZpAxWoZa6pO7Ka3TjurxXArY++HVcEvaBu ZjuiFYJon7KWswRDIoM1BxRcHXNWA7M= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1743685629; 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=1iuQSaorUWabAgc6jDeLPIp1/uUYmPqoK+E2pdwgDEo=; b=207CdiegPooCFCMoIgPpQyyIqXPAYf3ImTlQrUkgNwJyYAEtArQEritCvftbqkzkA4E7q+ mC5OpFOvxb8SiHDg== 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 BE6F613A2C; Thu, 3 Apr 2025 13:07:08 +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 yoDpHvyH7mcIOwAAD6G6ig (envelope-from ); Thu, 03 Apr 2025 13:07:08 +0000 From: Fabiano Rosas To: Prasad Pandit Cc: qemu-devel@nongnu.org, peterx@redhat.com, berrange@redhat.com Subject: Re: [PATCH v8 7/7] migration/ram: Implement save_postcopy_prepare() In-Reply-To: References: <20250318123846.1370312-1-ppandit@redhat.com> <20250318123846.1370312-8-ppandit@redhat.com> <87semtkz32.fsf@suse.de> Date: Thu, 03 Apr 2025 10:07:05 -0300 Message-ID: <8734epl7gm.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 5B9E721180 X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCPT_COUNT_THREE(0.00)[4]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from,2a07:de40:b281:106:10:150:64:167:received]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email, suse.de:dkim, suse.de:mid, imap1.dmz-prg2.suse.org:helo, imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action Received-SPF: pass client-ip=195.135.223.130; envelope-from=farosas@suse.de; helo=smtp-out1.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, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 Prasad Pandit writes: > Hi, > > On Mon, 31 Mar 2025 at 20:49, Fabiano Rosas wrote: >> > +static bool ram_save_postcopy_prepare(QEMUFile *f, void *opaque, Error **errp) >> > +{ >> > + int ret; >> > + >> > + if (migrate_multifd()) { >> > + /* >> > + * When multifd is enabled, source QEMU needs to make sure all the >> > + * pages queued before postcopy starts to be flushed. >> >> s/to be/have been/ >> >> > + * >> > + * Meanwhile, the load of these pages must happen before switching >> >> s/Meanwhile,// >> >> > + * to postcopy. It's because loading of guest pages (so far) in >> > + * multifd recv threads is still non-atomic, so the load cannot >> > + * happen with vCPUs running on destination side. >> > + * >> > + * This flush and sync will guarantee those pages loaded _before_ >> >> s/loaded/are loaded/ >> >> > + * postcopy starts on destination. The rational is, this happens >> >> s/rational/rationale/ >> >> > + * before VM stops (and before source QEMU sends all the rest of >> > + * the postcopy messages). So when the destination QEMU received >> > + * the postcopy messages, it must have received the sync message on >> > + * the main channel (either RAM_SAVE_FLAG_MULTIFD_FLUSH, or >> > + * RAM_SAVE_FLAG_EOS), and such message should have guaranteed all >> > + * previous guest pages queued in the multifd channels to be >> > + * completely loaded. >> > + */ > > * I'll include the above suggested corrections. I'm thinking it might > help more to have such an explanatory comment at the definition of the > multifd_ram_flush_and_sync() routine. Because looking at that function > it is not clear how 'MULTIFD_SYNC_ALL' is used. It sets the > '->pending_sync' to MULTIFD_SYNC_CALL. And when '->pending_sync' is > set this way, multifd_send_thread() writes 'MULTIFD_FLAG_SYNC' on each > multifd channel. At the destination this 'MULTIFD_FLAG_SYNC' flag is > then used to sync main and multifd_recv threads. > > ...wdyt? The code assumes some understanding of the multifd sync in general. It doesn't help that we don't have a high level documentation for that (yet). If you think the comments at the MultiFDSyncReq are not enough, feel free to propose a separate patch adding documentation to multifd_ram_flush_and_sync(). > > Thank you. > --- > - Prasad