From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37367) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fdgoh-0001LF-Mj for qemu-devel@nongnu.org; Thu, 12 Jul 2018 14:59:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fdgoe-0007I0-Fi for qemu-devel@nongnu.org; Thu, 12 Jul 2018 14:59:51 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:60278 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fdgoe-0007H2-8O for qemu-devel@nongnu.org; Thu, 12 Jul 2018 14:59:48 -0400 Date: Thu, 12 Jul 2018 19:59:43 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20180712185942.GF2610@work-vm> References: <20180629080320.320144-1-dplotnikov@virtuozzo.com> <20180629080320.320144-8-dplotnikov@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180629080320.320144-8-dplotnikov@virtuozzo.com> Subject: Re: [Qemu-devel] [PATCH v0 7/7] migration: add background snapshotting List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Denis Plotnikov Cc: quintela@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org * Denis Plotnikov (dplotnikov@virtuozzo.com) wrote: > The patch enables to save vmstate to a migration thread > in the background: ram is being saved while vCPUs are running. > This is done to reduce downtime on vm snapshotting: the majority > of vmstate is ram, the rest of devices consumes only a few MB of > memory on a typical vm. > By this moment, there were no means to make a snapshot without > full vm stopping. From now, one can save a vm state having the vm > stopped only for a couple of seconds to save devices' states. Then > the vm resumed and ram is written without the vm full stopping. > > To use async vm state it's needed to enable "background-snapshot" > migration capability and start the migration. > > Signed-off-by: Denis Plotnikov > --- > migration/migration.c | 104 +++++++++++++++++++++++++++++++++++++++++- > migration/savevm.c | 91 +++++++++++++++++++----------------- > migration/savevm.h | 2 + > 3 files changed, 154 insertions(+), 43 deletions(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 131d0904e4..b062bd8ddc 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -2188,6 +2188,100 @@ bool migrate_colo_enabled(void) > return s->enabled_capabilities[MIGRATION_CAPABILITY_X_COLO]; > } > > +static void background_snapshot_sigsegv_handler(int unused0, siginfo_t *info, void *unused1) > +{ > + if (ram_process_page_fault(info->si_addr)) { > + assert(false); > + } > +} > + > +static void *background_snapshot_thread(void *opaque) > +{ > + MigrationState *m = opaque; > + QIOChannelBuffer *bioc; > + QEMUFile *fb; > + RamBlockList *ram_blocks; > + int res = 0; > + > + rcu_register_thread(); > + > + qemu_file_set_rate_limit(m->to_dst_file, INT64_MAX); > + > + qemu_mutex_lock_iothread(); > + vm_stop(RUN_STATE_PAUSED); > + > + qemu_savevm_state_header(m->to_dst_file); > + qemu_mutex_unlock_iothread(); > + qemu_savevm_state_setup(m->to_dst_file); > + qemu_mutex_lock_iothread(); That's curiously different locking from the ones in migration.c and savevm.c (qemu_savevm_state) > + migrate_set_state(&m->state, MIGRATION_STATUS_SETUP, > + MIGRATION_STATUS_ACTIVE); > + > + // save the device state to the temporary buffer > + bioc = qio_channel_buffer_new(4096); > + qio_channel_set_name(QIO_CHANNEL(bioc), "vmstate-buffer"); > + fb = qemu_fopen_channel_output(QIO_CHANNEL(bioc)); > + object_unref(OBJECT(bioc)); > + > + ram_blocks = ram_blocks_get(); > + ram_blocks_fill(ram_blocks); > + ram_blocks_set_ro(ram_blocks); > + > + if(global_state_store()) { > + goto exit; > + } > + > + if (qemu_save_all_device_states(fb, false, true) < 0) { > + migrate_set_state(&m->state, MIGRATION_STATUS_ACTIVE, > + MIGRATION_STATUS_FAILED); > + goto exit; > + } > + > + sigsegv_user_handler_set(background_snapshot_sigsegv_handler); That's actually a good test if you're write protecting the RAM before saving the device state; they *shouldn't* write to ram doing that but I don't trust them. > + smp_mb(); Comment why that mb is there? > + vm_start(); > + qemu_mutex_unlock_iothread(); > + > + while (!res) { > + res = qemu_savevm_state_iterate(m->to_dst_file, false); I'm surprised it goes around this loop much, given that you've set hte bandwidth to max and I assume you never see dirty pages. > + if (res < 0 || qemu_file_get_error(m->to_dst_file)) { > + migrate_set_state(&m->state, MIGRATION_STATUS_ACTIVE, > + MIGRATION_STATUS_FAILED); > + goto exit; > + } > + } > + > + // By this moment we have RAM saved into the stream > + // The next step is to flush the device state right after the > + // RAM saved. The rest of device state is stored in > + // the temporary buffer. Let's flush the buffer into the stream. > + qemu_put_buffer(m->to_dst_file, bioc->data, bioc->usage); > + qemu_fflush(m->to_dst_file); > + > + if (qemu_file_get_error(m->to_dst_file)) { > + migrate_set_state(&m->state, MIGRATION_STATUS_ACTIVE, > + MIGRATION_STATUS_FAILED); > + goto exit; > + } > + > + migrate_set_state(&m->state, MIGRATION_STATUS_ACTIVE, > + MIGRATION_STATUS_COMPLETED); > +exit: > + ram_blocks_set_rw(ram_blocks); > + ram_blocks_clear(ram_blocks); > + smp_mb(); > + sigsegv_user_handler_reset(); > + qemu_fclose(fb); > + qemu_mutex_lock_iothread(); > + qemu_savevm_state_cleanup(); > + qemu_mutex_unlock_iothread(); > + rcu_unregister_thread(); > + return NULL; > +} > + > /* > * Master migration thread on the source VM. > * It drives the migration and pumps the data down the outgoing channel. > @@ -2402,8 +2496,14 @@ void migrate_fd_connect(MigrationState *s) > migrate_fd_cleanup(s); > return; > } > - qemu_thread_create(&s->thread, "live_migration", migration_thread, s, > - QEMU_THREAD_JOINABLE); > + if (migrate_background_snapshot()) { > + qemu_thread_create(&s->thread, "bg_snapshot", > + background_snapshot_thread, s, > + QEMU_THREAD_JOINABLE); > + } else { > + qemu_thread_create(&s->thread, "live_migration", migration_thread, s, > + QEMU_THREAD_JOINABLE); > + } > s->migration_thread_running = true; > } > > diff --git a/migration/savevm.c b/migration/savevm.c > index f202c3de3a..641b897ff5 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -1107,51 +1107,15 @@ void qemu_savevm_state_complete_postcopy(QEMUFile *f) > qemu_fflush(f); > } > > -int qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only, > - bool inactivate_disks) > +int qemu_save_all_device_states(QEMUFile *f, bool inactivate_disks, > + bool send_eof) We've got qemu_save_device_state as well; lots of variations. Dave > { > - QJSON *vmdesc; > int vmdesc_len; > SaveStateEntry *se; > int ret; > - bool in_postcopy = migration_in_postcopy(); > - > - trace_savevm_state_complete_precopy(); > + QJSON *vmdesc = qjson_new(); > > cpu_synchronize_all_states(); > - > - QTAILQ_FOREACH(se, &savevm_state.handlers, entry) { > - if (!se->ops || > - (in_postcopy && se->ops->has_postcopy && > - se->ops->has_postcopy(se->opaque)) || > - (in_postcopy && !iterable_only) || > - !se->ops->save_live_complete_precopy) { > - continue; > - } > - > - if (se->ops && se->ops->is_active) { > - if (!se->ops->is_active(se->opaque)) { > - continue; > - } > - } > - trace_savevm_section_start(se->idstr, se->section_id); > - > - save_section_header(f, se, QEMU_VM_SECTION_END); > - > - ret = se->ops->save_live_complete_precopy(f, se->opaque); > - trace_savevm_section_end(se->idstr, se->section_id, ret); > - save_section_footer(f, se); > - if (ret < 0) { > - qemu_file_set_error(f, ret); > - return -1; > - } > - } > - > - if (iterable_only) { > - return 0; > - } > - > - vmdesc = qjson_new(); > json_prop_int(vmdesc, "page_size", qemu_target_page_size()); > json_start_array(vmdesc, "devices"); > QTAILQ_FOREACH(se, &savevm_state.handlers, entry) { > @@ -1193,8 +1157,8 @@ int qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only, > return ret; > } > } > - if (!in_postcopy) { > - /* Postcopy stream will still be going */ > + > + if (send_eof) { > qemu_put_byte(f, QEMU_VM_EOF); > } > > @@ -1213,6 +1177,51 @@ int qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only, > return 0; > } > > +int qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only, > + bool inactivate_disks) > +{ > + SaveStateEntry *se; > + int ret; > + bool in_postcopy = migration_in_postcopy(); > + > + trace_savevm_state_complete_precopy(); > + > + cpu_synchronize_all_states(); > + > + QTAILQ_FOREACH(se, &savevm_state.handlers, entry) { > + if (!se->ops || > + (in_postcopy && se->ops->has_postcopy && > + se->ops->has_postcopy(se->opaque)) || > + (in_postcopy && !iterable_only) || > + !se->ops->save_live_complete_precopy) { > + continue; > + } > + > + if (se->ops && se->ops->is_active) { > + if (!se->ops->is_active(se->opaque)) { > + continue; > + } > + } > + trace_savevm_section_start(se->idstr, se->section_id); > + > + save_section_header(f, se, QEMU_VM_SECTION_END); > + > + ret = se->ops->save_live_complete_precopy(f, se->opaque); > + trace_savevm_section_end(se->idstr, se->section_id, ret); > + save_section_footer(f, se); > + if (ret < 0) { > + qemu_file_set_error(f, ret); > + return -1; > + } > + } > + > + if (iterable_only) { > + return 0; > + } > + > + return qemu_save_all_device_states(f, inactivate_disks, !in_postcopy); > +} > + > /* Give an estimate of the amount left to be transferred, > * the result is split into the amount for units that can and > * for units that can't do postcopy. > diff --git a/migration/savevm.h b/migration/savevm.h > index 295c4a1f2c..87b278142d 100644 > --- a/migration/savevm.h > +++ b/migration/savevm.h > @@ -55,4 +55,6 @@ void qemu_savevm_send_postcopy_ram_discard(QEMUFile *f, const char *name, > int qemu_loadvm_state(QEMUFile *f); > void qemu_loadvm_state_cleanup(void); > > +int qemu_save_all_device_states(QEMUFile *f, bool inactivate_disks, > + bool send_eof); > #endif > -- > 2.17.0 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK