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

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

* Peter Xu (peterx@redhat.com) wrote:
> On Thu, Feb 03, 2022 at 03:19:48PM +0000, Dr. David Alan Gilbert wrote:
> > * 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.
> 
> I'll squash this into the patch:

Thanks

> ---8<---
> diff --git a/migration/migration.h b/migration/migration.h
> index 845be3463c..2a311fd8d6 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -72,7 +72,10 @@ 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 */
> +    /*
> +     * Used to sync thread creations.  Note that we can't create threads in
> +     * parallel with this sem.
> +     */
>      QemuSemaphore  thread_sync_sem;
>      /*
>       * Free at the start of the main state load, set as the main thread finishes
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 099d8ed478..1a3ba1db84 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -79,6 +79,10 @@ int postcopy_notify(enum PostcopyNotifyReason reason, Error **errp)
>                                              &pnd);
>  }
>  
> +/*
> + * NOTE: this routine is not thread safe, we can't call it concurrently. But it
> + * should be good enough for migration's purposes.
> + */
>  void postcopy_thread_create(MigrationIncomingState *mis,
>                              QemuThread *thread, const char *name,
>                              void *(*fn)(void *), int joinable)
> ---8<---
> 
> > 
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> Thanks,
> 
> -- 
> Peter Xu
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK