Re: [Qemu-devel] [PATCH v7 14/42] Return path: Send responses from destination to source

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

* Juan Quintela (quintela@redhat.com) wrote:
> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> >
> > Add migrate_send_rp_message to send a message from destination to source along the return path.
> >   (It uses a mutex to let it be called from multiple threads)
> > Add migrate_send_rp_shut to send a 'shut' message to indicate
> >   the destination is finished with the RP.
> > Add migrate_send_rp_ack to send a 'PONG' message in response to a PING
> >   Use it in the MSG_RP_PING handler
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  include/migration/migration.h | 17 ++++++++++++++++
> >  migration/migration.c         | 45 +++++++++++++++++++++++++++++++++++++++++++
> >  migration/savevm.c            |  2 +-
> >  trace-events                  |  1 +
> >  4 files changed, 64 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index 65fe5db..36caab9 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -42,12 +42,20 @@ struct MigrationParams {
> >      bool shared;
> >  };
> >  
> > +/* Messages sent on the return path from destination to source */
> > +enum mig_rp_message_type {
> > +    MIG_RP_MSG_INVALID = 0,  /* Must be 0 */
> > +    MIG_RP_MSG_SHUT,         /* sibling will not send any more RP messages */
> > +    MIG_RP_MSG_PONG,         /* Response to a PING; data (seq: be32 ) */
> > +};
> > +
> >  typedef QLIST_HEAD(, LoadStateEntry) LoadStateEntry_Head;
> >  /* State for the incoming migration */
> >  struct MigrationIncomingState {
> >      QEMUFile *file;
> >  
> >      QEMUFile *return_path;
> > +    QemuMutex      rp_mutex;    /* We send replies from multiple threads */
> >  
> >      /* See savevm.c */
> >      LoadStateEntry_Head loadvm_handlers;
> > @@ -179,6 +187,15 @@ int migrate_compress_level(void);
> >  int migrate_compress_threads(void);
> >  int migrate_decompress_threads(void);
> >  
> > +/* Sending on the return path - generic and then for each message type */
> > +void migrate_send_rp_message(MigrationIncomingState *mis,
> > +                             enum mig_rp_message_type message_type,
> > +                             uint16_t len, void *data);
> > +void migrate_send_rp_shut(MigrationIncomingState *mis,
> > +                          uint32_t value);
> > +void migrate_send_rp_pong(MigrationIncomingState *mis,
> > +                          uint32_t value);
> > +
> >  void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
> >  void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
> >  void ram_control_load_hook(QEMUFile *f, uint64_t flags);
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 295f15a..afb19a1 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -85,6 +85,7 @@ MigrationIncomingState *migration_incoming_state_new(QEMUFile* f)
> >      mis_current = g_malloc0(sizeof(MigrationIncomingState));
> >      mis_current->file = f;
> >      QLIST_INIT(&mis_current->loadvm_handlers);
> > +    qemu_mutex_init(&mis_current->rp_mutex);
> >  
> >      return mis_current;
> >  }
> > @@ -182,6 +183,50 @@ void process_incoming_migration(QEMUFile *f)
> >      qemu_coroutine_enter(co, f);
> >  }
> >  
> > +/*
> > + * Send a message on the return channel back to the source
> > + * of the migration.
> > + */
> > +void migrate_send_rp_message(MigrationIncomingState *mis,
> > +                             enum mig_rp_message_type message_type,
> > +                             uint16_t len, void *data)
> > +{
> > +    trace_migrate_send_rp_message((int)message_type, len);
> > +    qemu_mutex_lock(&mis->rp_mutex);
> > +    qemu_put_be16(mis->return_path, (unsigned int)message_type);
> > +    qemu_put_be16(mis->return_path, len);
> if (len) {
> 
> > +    qemu_put_buffer(mis->return_path, data, len);
> }
> 
> 
> ?
> 
> We check for zero sized command on control commands but not on
> responses?

Or should I remove the check in the control commands case?
qemu_put_buffer looks like it's safe for size == 0

Dave

> 
> > +    qemu_fflush(mis->return_path);
> > +    qemu_mutex_unlock(&mis->rp_mutex);
> > +}
> > +
> > +/*
> > + * Send a 'SHUT' message on the return channel with the given value
> > + * to indicate that we've finished with the RP.  Non-0 value indicates
> > + * error.
> > + */
> > +void migrate_send_rp_shut(MigrationIncomingState *mis,
> > +                          uint32_t value)
> > +{
> > +    uint32_t buf;
> > +
> > +    buf = cpu_to_be32(value);
> > +    migrate_send_rp_message(mis, MIG_RP_MSG_SHUT, sizeof(buf), &buf);
> > +}
> > +
> > +/*
> > + * Send a 'PONG' message on the return channel with the given value
> > + * (normally in response to a 'PING')
> > + */
> > +void migrate_send_rp_pong(MigrationIncomingState *mis,
> > +                          uint32_t value)
> > +{
> > +    uint32_t buf;
> > +
> > +    buf = cpu_to_be32(value);
> > +    migrate_send_rp_message(mis, MIG_RP_MSG_PONG, sizeof(buf), &buf);
> > +}
> > +
> >  /* amount of nanoseconds we are willing to wait for migration to be down.
> >   * the choice of nanoseconds is because it is the maximum resolution that
> >   * get_clock() can achieve. It is an internal measure. All user-visible
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index a995014..d424c2a 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -1071,7 +1071,7 @@ static int loadvm_process_command(QEMUFile *f)
> >                           tmp32);
> >              return -1;
> >          }
> > -        /* migrate_send_rp_pong(mis, tmp32); TODO: gets added later */
> > +        migrate_send_rp_pong(mis, tmp32);
> >          break;
> >  
> >      default:
> > diff --git a/trace-events b/trace-events
> > index 5967fdf..5738e3f 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1399,6 +1399,7 @@ migrate_fd_cleanup(void) ""
> >  migrate_fd_error(void) ""
> >  migrate_fd_cancel(void) ""
> >  migrate_pending(uint64_t size, uint64_t max) "pending size %" PRIu64 " max %" PRIu64
> > +migrate_send_rp_message(int msg_type, uint16_t len) "%d: len %d"
> >  migrate_transferred(uint64_t tranferred, uint64_t time_spent, double bandwidth, uint64_t size) "transferred %" PRIu64 " time_spent %" PRIu64 " bandwidth %g max_size %" PRId64
> >  
> >  # migration/rdma.c
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK