Re: [PATCH RFC 09/15] migration: Add postcopy_thread_create()

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

* Peter Xu (peterx@redhat.com) wrote:
> Postcopy create threads. A common manner is we init a sem and use it to sync
> with the thread.  Namely, we have fault_thread_sem and listen_thread_sem and
> they're only used for this.
> 
> Make it a shared infrastructure so it's easier to create yet another thread.
> 

It might be worth a note saying you now share that sem, so you can't
start two threads in parallel.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/migration.h    |  5 ++---
>  migration/postcopy-ram.c | 19 +++++++++++++------
>  migration/postcopy-ram.h |  4 ++++
>  migration/savevm.c       | 12 +++---------
>  4 files changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/migration/migration.h b/migration/migration.h
> index 8bb2931312..35e7f7babe 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -70,7 +70,8 @@ struct MigrationIncomingState {
>      /* A hook to allow cleanup at the end of incoming migration */
>      void *transport_data;
>      void (*transport_cleanup)(void *data);
> -
> +    /* Used to sync thread creations */
> +    QemuSemaphore  thread_sync_sem;
>      /*
>       * Free at the start of the main state load, set as the main thread finishes
>       * loading state.
> @@ -83,13 +84,11 @@ struct MigrationIncomingState {
>      size_t         largest_page_size;
>      bool           have_fault_thread;
>      QemuThread     fault_thread;
> -    QemuSemaphore  fault_thread_sem;
>      /* Set this when we want the fault thread to quit */
>      bool           fault_thread_quit;
>  
>      bool           have_listen_thread;
>      QemuThread     listen_thread;
> -    QemuSemaphore  listen_thread_sem;
>  
>      /* For the kernel to send us notifications */
>      int       userfault_fd;
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index d78e1b9373..88c832eeba 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -77,6 +77,16 @@ int postcopy_notify(enum PostcopyNotifyReason reason, Error **errp)
>                                              &pnd);
>  }
>  
> +void postcopy_thread_create(MigrationIncomingState *mis,
> +                            QemuThread *thread, const char *name,
> +                            void *(*fn)(void *), int joinable)
> +{
> +    qemu_sem_init(&mis->thread_sync_sem, 0);
> +    qemu_thread_create(thread, name, fn, mis, joinable);
> +    qemu_sem_wait(&mis->thread_sync_sem);
> +    qemu_sem_destroy(&mis->thread_sync_sem);
> +}
> +
>  /* Postcopy needs to detect accesses to pages that haven't yet been copied
>   * across, and efficiently map new pages in, the techniques for doing this
>   * are target OS specific.
> @@ -901,7 +911,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
>      trace_postcopy_ram_fault_thread_entry();
>      rcu_register_thread();
>      mis->last_rb = NULL; /* last RAMBlock we sent part of */
> -    qemu_sem_post(&mis->fault_thread_sem);
> +    qemu_sem_post(&mis->thread_sync_sem);
>  
>      struct pollfd *pfd;
>      size_t pfd_len = 2 + mis->postcopy_remote_fds->len;
> @@ -1172,11 +1182,8 @@ int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
>          return -1;
>      }
>  
> -    qemu_sem_init(&mis->fault_thread_sem, 0);
> -    qemu_thread_create(&mis->fault_thread, "postcopy/fault",
> -                       postcopy_ram_fault_thread, mis, QEMU_THREAD_JOINABLE);
> -    qemu_sem_wait(&mis->fault_thread_sem);
> -    qemu_sem_destroy(&mis->fault_thread_sem);
> +    postcopy_thread_create(mis, &mis->fault_thread, "postcopy/fault",
> +                           postcopy_ram_fault_thread, QEMU_THREAD_JOINABLE);
>      mis->have_fault_thread = true;
>  
>      /* Mark so that we get notified of accesses to unwritten areas */
> diff --git a/migration/postcopy-ram.h b/migration/postcopy-ram.h
> index 6d2b3cf124..07684c0e1d 100644
> --- a/migration/postcopy-ram.h
> +++ b/migration/postcopy-ram.h
> @@ -135,6 +135,10 @@ void postcopy_remove_notifier(NotifierWithReturn *n);
>  /* Call the notifier list set by postcopy_add_start_notifier */
>  int postcopy_notify(enum PostcopyNotifyReason reason, Error **errp);
>  
> +void postcopy_thread_create(MigrationIncomingState *mis,
> +                            QemuThread *thread, const char *name,
> +                            void *(*fn)(void *), int joinable);
> +
>  struct PostCopyFD;
>  
>  /* ufd is a pointer to the struct uffd_msg *TODO: more Portable! */
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 3b8f565b14..3342b74c24 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1862,7 +1862,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
>  
>      migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
>                                     MIGRATION_STATUS_POSTCOPY_ACTIVE);
> -    qemu_sem_post(&mis->listen_thread_sem);
> +    qemu_sem_post(&mis->thread_sync_sem);
>      trace_postcopy_ram_listen_thread_start();
>  
>      rcu_register_thread();
> @@ -1987,14 +1987,8 @@ static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
>      }
>  
>      mis->have_listen_thread = true;
> -    /* Start up the listening thread and wait for it to signal ready */
> -    qemu_sem_init(&mis->listen_thread_sem, 0);
> -    qemu_thread_create(&mis->listen_thread, "postcopy/listen",
> -                       postcopy_ram_listen_thread, NULL,
> -                       QEMU_THREAD_DETACHED);
> -    qemu_sem_wait(&mis->listen_thread_sem);
> -    qemu_sem_destroy(&mis->listen_thread_sem);
> -
> +    postcopy_thread_create(mis, &mis->listen_thread, "postcopy/listen",
> +                           postcopy_ram_listen_thread, QEMU_THREAD_DETACHED);
>      trace_loadvm_postcopy_handle_listen("return");
>  
>      return 0;
> -- 
> 2.32.0
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK