Re: [Qemu-devel] [PATCH 11/17] migration: Create thread infrastructure for multifd send side

[Paolo Bonzini]

On 23/01/2017 22:32, Juan Quintela wrote:
> We make the locking and the transfer of information specific, even if we
> are still transmiting things through the main thread.
> 
> Signed-off-by: Juan Quintela <address@hidden>
> ---
>  migration/ram.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index c71929e..9d7bc64 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -392,17 +392,25 @@ void migrate_compress_threads_create(void)
>  /* Multiple fd's */
> 
>  struct MultiFDSendParams {
> +    /* not changed */
>      QemuThread thread;
>      QIOChannel *c;
>      QemuCond cond;
>      QemuMutex mutex;
> +    /* protected by param mutex */
>      bool quit;
>      bool started;
> +    uint8_t *address;
> +    /* protected by multifd mutex */
> +    bool done;
>  };
>  typedef struct MultiFDSendParams MultiFDSendParams;
> 
>  static MultiFDSendParams *multifd_send;
> 
> +QemuMutex multifd_send_mutex;
> +QemuCond multifd_send_cond;

Having n+1 semaphores instead of n+1 cond/mutex pairs could be more
efficient.  See thread-pool.c for an example.

Paolo

>  static void *multifd_send_thread(void *opaque)
>  {
>      MultiFDSendParams *params = opaque;
> @@ -416,7 +424,17 @@ static void *multifd_send_thread(void *opaque)
> 
>      qemu_mutex_lock(&params->mutex);
>      while (!params->quit){
> -        qemu_cond_wait(&params->cond, &params->mutex);
> +        if (params->address) {
> +            params->address = 0;
> +            qemu_mutex_unlock(&params->mutex);
> +            qemu_mutex_lock(&multifd_send_mutex);
> +            params->done = true;
> +            qemu_cond_signal(&multifd_send_cond);
> +            qemu_mutex_unlock(&multifd_send_mutex);
> +            qemu_mutex_lock(&params->mutex);
> +        } else {
> +            qemu_cond_wait(&params->cond, &params->mutex);
> +        }
>      }
>      qemu_mutex_unlock(&params->mutex);
> 
> @@ -464,12 +482,16 @@ void migrate_multifd_send_threads_create(void)
>      }
>      thread_count = migrate_multifd_threads();
>      multifd_send = g_new0(MultiFDSendParams, thread_count);
> +    qemu_mutex_init(&multifd_send_mutex);
> +    qemu_cond_init(&multifd_send_cond);
>      for (i = 0; i < thread_count; i++) {
>          char thread_name[15];
>          qemu_mutex_init(&multifd_send[i].mutex);
>          qemu_cond_init(&multifd_send[i].cond);
>          multifd_send[i].quit = false;
>          multifd_send[i].started = false;
> +        multifd_send[i].done = true;
> +        multifd_send[i].address = 0;
>          multifd_send[i].c = socket_send_channel_create();
>          if(!multifd_send[i].c) {
>              error_report("Error creating a send channel");
> @@ -487,6 +509,34 @@ void migrate_multifd_send_threads_create(void)
>      }
>  }
> 
> +static int multifd_send_page(uint8_t *address)
> +{
> +    int i, thread_count;
> +    bool found = false;
> +
> +    thread_count = migrate_multifd_threads();
> +    qemu_mutex_lock(&multifd_send_mutex);
> +    while (!found) {
> +        for (i = 0; i < thread_count; i++) {
> +            if (multifd_send[i].done) {
> +                multifd_send[i].done = false;
> +                found = true;
> +                break;
> +            }
> +        }
> +        if (!found) {
> +            qemu_cond_wait(&multifd_send_cond, &multifd_send_mutex);
> +        }
> +    }
> +    qemu_mutex_unlock(&multifd_send_mutex);
> +    qemu_mutex_lock(&multifd_send[i].mutex);
> +    multifd_send[i].address = address;
> +    qemu_cond_signal(&multifd_send[i].cond);
> +    qemu_mutex_unlock(&multifd_send[i].mutex);
> +
> +    return 0;
> +}
> +
>  struct MultiFDRecvParams {
>      QemuThread thread;
>      QIOChannel *c;
> @@ -1015,6 +1065,7 @@ static int ram_multifd_page(QEMUFile *f, 
> PageSearchStatus *pss,
>          *bytes_transferred +=
>              save_page_header(f, block, offset | RAM_SAVE_FLAG_MULTIFD_PAGE);
>          qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
> +        multifd_send_page(p);
>          *bytes_transferred += TARGET_PAGE_SIZE;
>          pages = 1;
>          acct_info.norm_pages++;
>