Re: [Qemu-devel] [PATCH 3/6] migration: Make sure that all multifd channels have been created

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Juan Quintela (quintela@redhat.com) wrote:
> If we start the migration before all have been created, we have to
> handle the case that one channel still don't exist.  This way it is
> easier.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/ram.c        | 14 ++++++++++++++
>  migration/trace-events |  1 +
>  2 files changed, 15 insertions(+)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 4bdd201a4e..4a6ae677a9 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -663,6 +663,8 @@ typedef struct {
>      uint64_t num_pages;
>      /* syncs main thread and channels */
>      QemuSemaphore sem_sync;
> +    /* thread has started and setup is done */
> +    QemuSemaphore started;
>  }  MultiFDSendParams;
>  
>  typedef struct {
> @@ -1039,6 +1041,7 @@ void multifd_save_cleanup(void)
>          qemu_mutex_destroy(&p->mutex);
>          qemu_sem_destroy(&p->sem);
>          qemu_sem_destroy(&p->sem_sync);
> +        qemu_sem_destroy(&p->started);
>          g_free(p->name);
>          p->name = NULL;
>          multifd_pages_clear(p->pages);
> @@ -1113,6 +1116,8 @@ static void *multifd_send_thread(void *opaque)
>      /* initial packet */
>      p->num_packets = 1;
>  
> +    qemu_sem_post(&p->started);
> +
>      while (true) {
>          qemu_sem_wait(&p->sem);
>          qemu_mutex_lock(&p->mutex);
> @@ -1229,6 +1234,7 @@ int multifd_save_setup(void)
>          qemu_mutex_init(&p->mutex);
>          qemu_sem_init(&p->sem, 0);
>          qemu_sem_init(&p->sem_sync, 0);
> +        qemu_sem_init(&p->started, 0);
>          p->quit = false;
>          p->pending_job = 0;
>          p->id = i;
> @@ -3486,6 +3492,14 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>      ram_control_before_iterate(f, RAM_CONTROL_SETUP);
>      ram_control_after_iterate(f, RAM_CONTROL_SETUP);
>  
> +    /* We want to wait for all threads to have started before doing
> +     * anything else */
> +    for (int i = 0; i < migrate_multifd_channels(); i++) {
> +        MultiFDSendParams *p = &multifd_send_state->params[i];
> +
> +        qemu_sem_wait(&p->started);
> +        trace_multifd_send_thread_started(p->id);
> +    }

What happens if there's an error during startup and either we cancel or
the migration fails and we try and cleanup - how do we get out of this
loop?

Dave

>      multifd_send_sync_main();
>      qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
>      qemu_fflush(f);
> diff --git a/migration/trace-events b/migration/trace-events
> index 886ce70ca0..dd13a5c4b1 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -95,6 +95,7 @@ multifd_send_sync_main_wait(uint8_t id) "channel %d"
>  multifd_send_terminate_threads(bool error) "error %d"
>  multifd_send_thread_end(uint8_t id, uint64_t packets, uint64_t pages) "channel %d packets %" PRIu64 " pages %"  PRIu64
>  multifd_send_thread_start(uint8_t id) "%d"
> +multifd_send_thread_started(uint8_t id) "channel %d"
>  ram_discard_range(const char *rbname, uint64_t start, size_t len) "%s: start: %" PRIx64 " %zx"
>  ram_load_loop(const char *rbname, uint64_t addr, int flags, void *host) "%s: addr: 0x%" PRIx64 " flags: 0x%x host: %p"
>  ram_load_postcopy_loop(uint64_t addr, int flags) "@%" PRIx64 " %x"
> -- 
> 2.21.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK