Re: [Qemu-devel] [PATCH v5 11/17] migration: Really use multiple pages at a time

[Dr. David Alan Gilbert]

* Juan Quintela (address@hidden) wrote:
> We now send several pages at a time each time that we wakeup a thread.
> 
> Signed-off-by: Juan Quintela <address@hidden>
> 
> --
> 
> Use iovec's insead of creating the equivalent.
> ---
>  migration/ram.c | 46 ++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 40 insertions(+), 6 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 2bf3fa7..90e1bcb 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -362,6 +362,13 @@ static void compress_threads_save_setup(void)
>  
>  /* Multiple fd's */
>  
> +
> +typedef struct {
> +    int num;
> +    int size;

size_t ?

> +    struct iovec *iov;
> +} multifd_pages_t;
> +
>  struct MultiFDSendParams {
>      /* not changed */
>      uint8_t id;
> @@ -371,7 +378,7 @@ struct MultiFDSendParams {
>      QemuMutex mutex;
>      /* protected by param mutex */
>      bool quit;
> -    uint8_t *address;
> +    multifd_pages_t pages;
>      /* protected by multifd mutex */
>      bool done;
>  };
> @@ -459,8 +466,8 @@ static void *multifd_send_thread(void *opaque)
>              qemu_mutex_unlock(&p->mutex);
>              break;
>          }
> -        if (p->address) {
> -            p->address = 0;
> +        if (p->pages.num) {
> +            p->pages.num = 0;
>              qemu_mutex_unlock(&p->mutex);
>              qemu_mutex_lock(&multifd_send_state->mutex);
>              p->done = true;
> @@ -475,6 +482,13 @@ static void *multifd_send_thread(void *opaque)
>      return NULL;
>  }
>  
> +static void multifd_init_group(multifd_pages_t *pages)
> +{
> +    pages->num = 0;
> +    pages->size = migrate_multifd_group();
> +    pages->iov = g_malloc0(pages->size * sizeof(struct iovec));

Does that get freed anywhere?

> +}
> +
>  int multifd_save_setup(void)
>  {
>      int thread_count;
> @@ -498,7 +512,7 @@ int multifd_save_setup(void)
>          p->quit = false;
>          p->id = i;
>          p->done = true;
> -        p->address = 0;
> +        multifd_init_group(&p->pages);
>          p->c = socket_send_channel_create();
>          if (!p->c) {
>              error_report("Error creating a send channel");
> @@ -515,8 +529,23 @@ int multifd_save_setup(void)
>  
>  static int multifd_send_page(uint8_t *address)
>  {
> -    int i;
> +    int i, j;
>      MultiFDSendParams *p = NULL; /* make happy gcc */
> +    static multifd_pages_t pages;
> +    static bool once;
> +
> +    if (!once) {
> +        multifd_init_group(&pages);
> +        once = true;
> +    }
> +
> +    pages.iov[pages.num].iov_base = address;
> +    pages.iov[pages.num].iov_len = TARGET_PAGE_SIZE;
> +    pages.num++;
> +
> +    if (pages.num < (pages.size - 1)) {
> +        return UINT16_MAX;

That's a very odd magic constant to return.
What's your intention?

> +    }
>  
>      qemu_sem_wait(&multifd_send_state->sem);
>      qemu_mutex_lock(&multifd_send_state->mutex);
> @@ -530,7 +559,12 @@ static int multifd_send_page(uint8_t *address)
>      }
>      qemu_mutex_unlock(&multifd_send_state->mutex);
>      qemu_mutex_lock(&p->mutex);
> -    p->address = address;
> +    p->pages.num = pages.num;
> +    for (j = 0; j < pages.size; j++) {
> +        p->pages.iov[j].iov_base = pages.iov[j].iov_base;
> +        p->pages.iov[j].iov_len = pages.iov[j].iov_len;
> +    }

It would seem more logical to update p->pages.num last

This is also a little odd in that iov_len is never really used,
it's always TARGET_PAGE_SIZE.

> +    pages.num = 0;
>      qemu_mutex_unlock(&p->mutex);
>      qemu_sem_post(&p->sem);

What makes sure that any final chunk of pages that was less
than the group size is sent at the end?

Dave

> -- 
> 2.9.4
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK