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Thu, 1 Feb 2024 21:46:38 +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 wtwMCT4RvGXCXgAAD6G6ig (envelope-from ); Thu, 01 Feb 2024 21:46:38 +0000 From: Fabiano Rosas To: Avihai Horon , Peter Xu Cc: qemu-devel@nongnu.org, Bryan Zhang , Prasad Pandit , Yuan Liu , Hao Xiang Subject: Re: [PATCH 00/14] migration/multifd: Refactor ->send_prepare() and cleanups In-Reply-To: <5515481b-3601-46e0-ba82-cbec056966f0@nvidia.com> References: <20240131103111.306523-1-peterx@redhat.com> <871q9xjey8.fsf@suse.de> <5515481b-3601-46e0-ba82-cbec056966f0@nvidia.com> Date: Thu, 01 Feb 2024 18:46:35 -0300 Message-ID: <87le83j1s4.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=ZgOuJEwq; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=It+5UKiX X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-5.51 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%]; MIME_GOOD(-0.10)[text/plain]; NEURAL_HAM_LONG(-1.00)[-1.000]; DWL_DNSWL_LOW(-1.00)[suse.de:dkim]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+]; MX_GOOD(-0.01)[]; RCPT_COUNT_SEVEN(0.00)[7]; DBL_BLOCKED_OPENRESOLVER(0.00)[nvidia.com:email,suse.de:dkim]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; NEURAL_HAM_SHORT(-0.20)[-1.000]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[] X-Rspamd-Queue-Id: D301F22132 Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:1; 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, 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 Avihai Horon writes: > On 01/02/2024 7:47, Peter Xu wrote: >> External email: Use caution opening links or attachments >> >> >> On Wed, Jan 31, 2024 at 07:49:51PM -0300, Fabiano Rosas wrote: >>> peterx@redhat.com writes: >>> >>>> From: Peter Xu >>>> >>>> This patchset contains quite a few refactorings to current multifd: >>>> >>>> - It picked up some patches from an old series of mine [0] (the last >>>> patches were dropped, though; I did the cleanup slightly differently): >>>> >>>> I still managed to include one patch to split pending_job, but I >>>> rewrote the patch here. >>>> >>>> - It tries to cleanup multiple multifd paths here and there, the ultimate >>>> goal is to redefine send_prepare() to be something like: >>>> >>>> p->pages -----------> send_prepare() -------------> IOVs >>>> >>>> So that there's no obvious change yet on multifd_ops besides redefined >>>> interface for send_prepare(). We may want a separate OPs for file >>>> later. >>>> >>>> For 2), one benefit is already presented by Fabiano in his other series [1] >>>> on cleaning up zero copy, but this patchset addressed it quite differently, >>>> and hopefully also more gradually. The other benefit is for sure if we >>>> have a more concrete API for send_prepare() and if we can reach an initial >>>> consensus, then we can have the recent compression accelerators rebased on >>>> top of this one. >>>> >>>> This also prepares for the case where the input can be extended to even not >>>> any p->pages, but arbitrary data (like VFIO's potential use case in the >>>> future?). But that will also for later even if reasonable. >>>> >>>> Please have a look. Thanks, >>>> >>>> [0] https://lore.kernel.org/r/20231022201211.452861-1-peterx@redhat.com >>>> [1] https://lore.kernel.org/qemu-devel/20240126221943.26628-1-farosas@suse.de >>>> >>>> Peter Xu (14): >>>> migration/multifd: Drop stale comment for multifd zero copy >>>> migration/multifd: multifd_send_kick_main() >>>> migration/multifd: Drop MultiFDSendParams.quit, cleanup error paths >>>> migration/multifd: Postpone reset of MultiFDPages_t >>>> migration/multifd: Drop MultiFDSendParams.normal[] array >>>> migration/multifd: Separate SYNC request with normal jobs >>>> migration/multifd: Simplify locking in sender thread >>>> migration/multifd: Drop pages->num check in sender thread >>>> migration/multifd: Rename p->num_packets and clean it up >>>> migration/multifd: Move total_normal_pages accounting >>>> migration/multifd: Move trace_multifd_send|recv() >>>> migration/multifd: multifd_send_prepare_header() >>>> migration/multifd: Move header prepare/fill into send_prepare() >>>> migration/multifd: Forbid spurious wakeups >>>> >>>> migration/multifd.h | 34 +++-- >>>> migration/multifd-zlib.c | 11 +- >>>> migration/multifd-zstd.c | 11 +- >>>> migration/multifd.c | 291 +++++++++++++++++++-------------------- >>>> 4 files changed, 182 insertions(+), 165 deletions(-) >>> This series didn't survive my 9999 iterations test on the opensuse >>> machine. >>> >>> # Running /x86_64/migration/multifd/tcp/tls/x509/reject-anon-client >>> ... >>> kill_qemu() detected QEMU death from signal 11 (Segmentation fault) (core dumped) >>> >>> >>> #0 0x00005575dda06399 in qemu_mutex_lock_impl (mutex=0x18, file=0x5575ddce9cc3 "../util/qemu-thread-posix.c", line=275) at ../util/qemu-thread-posix.c:92 >>> #1 0x00005575dda06a94 in qemu_sem_post (sem=0x18) at ../util/qemu-thread-posix.c:275 >>> #2 0x00005575dd56a512 in multifd_send_thread (opaque=0x5575df054ef8) at ../migration/multifd.c:720 >>> #3 0x00005575dda0709b in qemu_thread_start (args=0x7fd404001d50) at ../util/qemu-thread-posix.c:541 >>> #4 0x00007fd45e8a26ea in start_thread (arg=0x7fd3faffd700) at pthread_create.c:477 >>> #5 0x00007fd45cd2150f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95 >>> >>> The multifd thread is posting channels_ready with an already freed >>> multifd_send_state. >>> >>> This is the bug Avihai has hit. We're going into multifd_save_cleanup() >>> so early that multifd_new_send_channel_async() hasn't even had the >>> chance to set p->running. So it misses the join and frees everything up >>> while a second multifd thread is just starting. >> Thanks for doing that. >> >> Would this series makes that bug easier to happen? > > I think so. > Patch #3 added an extra multifd_send_should_exit() check in > multifd_send_sync_main(), so now it can exit early if the first channel > fails. > Plus, now migration state is set to FAILED early by: > multifd_new_send_channel_async()->multifd_send_terminate_threads() and > multifd_tls_outgoing_handshake()->multifd_send_terminate_threads() > so migration_iteration_run() is completely skipped because > migration_is_active() check before it will return false. > > I *think* this is what makes main migration thread finish earlier and > call multifd_save_cleanup() earlier, at least for me. > I'm doing some experiments with a global semaphore like channels_ready instead of a per-channel structure like you suggested. I think we only need to have a point past which we're assured no more channels will be created. With that we'd only need one post at multifd_new_send_channel_async.