On Tue, Jul 30, 2019 at 01:36:32PM +0800, Ivan Ren wrote: >From: Ivan Ren <ivan...@tencent.com> > >This patch fix a multifd migration bug in migration speed calculation, this >problem can be reproduced as follows: >1. start a vm and give a heavy memory write stress to prevent the vm be > successfully migrated to destination >2. begin a migration with multifd >3. migrate for a long time [actually, this can be measured by transferred >bytes] >4. migrate cancel >5. begin a new migration with multifd, the migration will directly run into > migration_completion phase > >Reason as follows: > >Migration update bandwidth and s->threshold_size in function >migration_update_counters after BUFFER_DELAY time: > > current_bytes = migration_total_bytes(s); > transferred = current_bytes - s->iteration_initial_bytes; > time_spent = current_time - s->iteration_start_time; > bandwidth = (double)transferred / time_spent; > s->threshold_size = bandwidth * s->parameters.downtime_limit; > >In multifd migration, migration_total_bytes function return >qemu_ftell(s->to_dst_file) + ram_counters.multifd_bytes. >s->iteration_initial_bytes will be initialized to 0 at every new migration, >but ram_counters is a global variable, and history migration data will be >accumulated. So if the ram_counters.multifd_bytes is big enough, it may lead >pending_size >= s->threshold_size become false in migration_iteration_run >after the first migration_update_counters. > >Signed-off-by: Ivan Ren <ivan...@tencent.com> >--- > migration/migration.c | 15 ++++++++++++++- > migration/savevm.c | 1 + > 2 files changed, 15 insertions(+), 1 deletion(-) > >diff --git a/migration/migration.c b/migration/migration.c >index 8a607fe1e2..d35a6ae6f9 100644 >--- a/migration/migration.c >+++ b/migration/migration.c >@@ -1908,6 +1908,11 @@ static bool migrate_prepare(MigrationState *s, bool >blk, bool blk_inc, > } > > migrate_init(s); >+ /* >+ * set ram_counters memory to zero for a >+ * new migration >+ */ >+ memset(&ram_counters, 0, sizeof(ram_counters)); > > return true; > } >@@ -3187,6 +3192,10 @@ static void *migration_thread(void *opaque) > > object_ref(OBJECT(s)); > s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); >+ /* >+ * Update s->iteration_initial_bytes to match s->iteration_start_time. >+ */ >+ s->iteration_initial_bytes = migration_total_bytes(s);
Is this one necessary? We have sent out nothing yet. > > qemu_savevm_state_header(s->to_dst_file); > >@@ -3252,7 +3261,11 @@ static void *migration_thread(void *opaque) > * breaking transferred_bytes and bandwidth calculation > */ > s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); >- s->iteration_initial_bytes = 0; >+ /* >+ * Update s->iteration_initial_bytes to current size to >+ * avoid historical data lead wrong bandwidth. >+ */ >+ s->iteration_initial_bytes = migration_total_bytes(s); > } > > current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); >diff --git a/migration/savevm.c b/migration/savevm.c >index 79ed44d475..480c511b19 100644 >--- a/migration/savevm.c >+++ b/migration/savevm.c >@@ -1424,6 +1424,7 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp) > } > > migrate_init(ms); >+ memset(&ram_counters, 0, sizeof(ram_counters)); > ms->to_dst_file = f; > > qemu_mutex_unlock_iothread(); >-- >2.17.2 (Apple Git-113) > -- Wei Yang Help you, Help me
