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migration: Wake rate limiting for urgent requests

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Rate limiting sleeps the migration thread for a while when it runs
out of bandwidth; but sometimes we want to wake up to get on with
something more urgent (like a postcopy request).  Here we use
a semaphore with a timedwait instead of a simple sleep; Incrementing
the sempahore will wake it up sooner.  Anything that consumes
these urgent events must decrement the sempahore.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20180613102642.23995-3-dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2018-06-13 11:26:41 +01:00
parent 7e555c6c58
commit ad767bed5a
3 changed files with 41 additions and 4 deletions
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35
migration/migration.c
View File

@ -2852,6 +2852,16 @@ static void migration_iteration_finish(MigrationState *s)
qemu_mutex_unlock_iothread();
}
void migration_make_urgent_request(void)
{
qemu_sem_post(&migrate_get_current()->rate_limit_sem);
}
void migration_consume_urgent_request(void)
{
qemu_sem_wait(&migrate_get_current()->rate_limit_sem);
}
/*
* Master migration thread on the source VM.
* It drives the migration and pumps the data down the outgoing channel.
@ -2861,6 +2871,7 @@ static void *migration_thread(void *opaque)
MigrationState *s = opaque;
int64_t setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
MigThrError thr_error;
bool urgent = false;
rcu_register_thread();
@ -2901,7 +2912,7 @@ static void *migration_thread(void *opaque)
s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
int64_t current_time;
if (!qemu_file_rate_limit(s->to_dst_file)) {
if (urgent || !qemu_file_rate_limit(s->to_dst_file)) {
MigIterateState iter_state = migration_iteration_run(s);
if (iter_state == MIG_ITERATE_SKIP) {
continue;
@ -2932,10 +2943,24 @@ static void *migration_thread(void *opaque)
migration_update_counters(s, current_time);
urgent = false;
if (qemu_file_rate_limit(s->to_dst_file)) {
/* usleep expects microseconds */
g_usleep((s->iteration_start_time + BUFFER_DELAY -
current_time) * 1000);
/* Wait for a delay to do rate limiting OR
* something urgent to post the semaphore.
*/
int ms = s->iteration_start_time + BUFFER_DELAY - current_time;
trace_migration_thread_ratelimit_pre(ms);
if (qemu_sem_timedwait(&s->rate_limit_sem, ms) == 0) {
/* We were worken by one or more urgent things but
* the timedwait will have consumed one of them.
* The service routine for the urgent wake will dec
* the semaphore itself for each item it consumes,
* so add this one we just eat back.
*/
qemu_sem_post(&s->rate_limit_sem);
urgent = true;
}
trace_migration_thread_ratelimit_post(urgent);
}
}
@ -3109,6 +3134,7 @@ static void migration_instance_finalize(Object *obj)
qemu_mutex_destroy(&ms->qemu_file_lock);
g_free(params->tls_hostname);
g_free(params->tls_creds);
qemu_sem_destroy(&ms->rate_limit_sem);
qemu_sem_destroy(&ms->pause_sem);
qemu_sem_destroy(&ms->postcopy_pause_sem);
qemu_sem_destroy(&ms->postcopy_pause_rp_sem);
@ -3147,6 +3173,7 @@ static void migration_instance_init(Object *obj)
qemu_sem_init(&ms->postcopy_pause_sem, 0);
qemu_sem_init(&ms->postcopy_pause_rp_sem, 0);
qemu_sem_init(&ms->rp_state.rp_sem, 0);
qemu_sem_init(&ms->rate_limit_sem, 0);
qemu_mutex_init(&ms->qemu_file_lock);
}

8
migration/migration.h
View File

@ -121,6 +121,11 @@ struct MigrationState
*/
QemuMutex qemu_file_lock;
/*
* Used to allow urgent requests to override rate limiting.
*/
QemuSemaphore rate_limit_sem;
/* bytes already send at the beggining of current interation */
uint64_t iteration_initial_bytes;
/* time at the start of current iteration */
@ -287,4 +292,7 @@ void init_dirty_bitmap_incoming_migration(void);
#define qemu_ram_foreach_block \
#warning "Use qemu_ram_foreach_block_migratable in migration code"
void migration_make_urgent_request(void);
void migration_consume_urgent_request(void);
#endif

2
migration/trace-events
View File

@ -108,6 +108,8 @@ migration_return_path_end_before(void) ""
migration_return_path_end_after(int rp_error) "%d"
migration_thread_after_loop(void) ""
migration_thread_file_err(void) ""
migration_thread_ratelimit_pre(int ms) "%d ms"
migration_thread_ratelimit_post(int urgent) "urgent: %d"
migration_thread_setup_complete(void) ""
open_return_path_on_source(void) ""
open_return_path_on_source_continue(void) ""