Re: [PATCH v4 2/8] migration/multifd: add get_iov_count in the multifd method

[Fabiano Rosas <farosas@suse.de>]

Yuan Liu <yuan1.liu@intel.com> writes:

> the new function get_iov_count is used to get the number of
> IOVs required by a specified multifd method
>
> Different multifd methods may require different numbers of IOVs.
> Based on streaming compression of zlib and zstd, all pages will be
> compressed to a data block, so an IOV is required to send this data
> block. For no compression, each IOV is used to send a page, so the
> number of IOVs required is the same as the number of pages.

Let's just move the responsibility of allocating p->iov to the client
code. You can move the allocation into send_setup() and the free into
send_cleanup().

>
> Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
> Reviewed-by: Nanhai Zou <nanhai.zou@intel.com>
> ---
>  migration/multifd-zlib.c | 18 +++++++++++++++++-
>  migration/multifd-zstd.c | 18 +++++++++++++++++-
>  migration/multifd.c      | 24 +++++++++++++++++++++---
>  migration/multifd.h      |  2 ++
>  4 files changed, 57 insertions(+), 5 deletions(-)
>
> diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c
> index 012e3bdea1..35187f2aff 100644
> --- a/migration/multifd-zlib.c
> +++ b/migration/multifd-zlib.c
> @@ -313,13 +313,29 @@ static int zlib_recv_pages(MultiFDRecvParams *p, Error **errp)
>      return 0;
>  }
>  
> +/**
> + * zlib_get_iov_count: get the count of IOVs
> + *
> + * For zlib streaming compression, all pages will be compressed into a data
> + * block, and an IOV is requested for sending this block.
> + *
> + * Returns the count of the IOVs
> + *
> + * @page_count: Indicate the maximum count of pages processed by multifd
> + */
> +static uint32_t zlib_get_iov_count(uint32_t page_count)
> +{
> +    return 1;
> +}
> +
>  static MultiFDMethods multifd_zlib_ops = {
>      .send_setup = zlib_send_setup,
>      .send_cleanup = zlib_send_cleanup,
>      .send_prepare = zlib_send_prepare,
>      .recv_setup = zlib_recv_setup,
>      .recv_cleanup = zlib_recv_cleanup,
> -    .recv_pages = zlib_recv_pages
> +    .recv_pages = zlib_recv_pages,
> +    .get_iov_count = zlib_get_iov_count
>  };
>  
>  static void multifd_zlib_register(void)
> diff --git a/migration/multifd-zstd.c b/migration/multifd-zstd.c
> index dc8fe43e94..25ed1add2a 100644
> --- a/migration/multifd-zstd.c
> +++ b/migration/multifd-zstd.c
> @@ -304,13 +304,29 @@ static int zstd_recv_pages(MultiFDRecvParams *p, Error **errp)
>      return 0;
>  }
>  
> +/**
> + * zstd_get_iov_count: get the count of IOVs
> + *
> + * For zstd streaming compression, all pages will be compressed into a data
> + * block, and an IOV is requested for sending this block.
> + *
> + * Returns the count of the IOVs
> + *
> + * @page_count: Indicate the maximum count of pages processed by multifd
> + */
> +static uint32_t zstd_get_iov_count(uint32_t page_count)
> +{
> +    return 1;
> +}
> +
>  static MultiFDMethods multifd_zstd_ops = {
>      .send_setup = zstd_send_setup,
>      .send_cleanup = zstd_send_cleanup,
>      .send_prepare = zstd_send_prepare,
>      .recv_setup = zstd_recv_setup,
>      .recv_cleanup = zstd_recv_cleanup,
> -    .recv_pages = zstd_recv_pages
> +    .recv_pages = zstd_recv_pages,
> +    .get_iov_count = zstd_get_iov_count
>  };
>  
>  static void multifd_zstd_register(void)
> diff --git a/migration/multifd.c b/migration/multifd.c
> index adfe8c9a0a..787402247e 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -209,13 +209,29 @@ static int nocomp_recv_pages(MultiFDRecvParams *p, Error **errp)
>      return qio_channel_readv_all(p->c, p->iov, p->normal_num, errp);
>  }
>  
> +/**
> + * nocomp_get_iov_count: get the count of IOVs
> + *
> + * For no compression, the count of IOVs required is the same as the count of
> + * pages
> + *
> + * Returns the count of the IOVs
> + *
> + * @page_count: Indicate the maximum count of pages processed by multifd
> + */
> +static uint32_t nocomp_get_iov_count(uint32_t page_count)
> +{
> +    return page_count;
> +}
> +
>  static MultiFDMethods multifd_nocomp_ops = {
>      .send_setup = nocomp_send_setup,
>      .send_cleanup = nocomp_send_cleanup,
>      .send_prepare = nocomp_send_prepare,
>      .recv_setup = nocomp_recv_setup,
>      .recv_cleanup = nocomp_recv_cleanup,
> -    .recv_pages = nocomp_recv_pages
> +    .recv_pages = nocomp_recv_pages,
> +    .get_iov_count = nocomp_get_iov_count
>  };
>  
>  static MultiFDMethods *multifd_ops[MULTIFD_COMPRESSION__MAX] = {
> @@ -998,6 +1014,8 @@ bool multifd_send_setup(void)
>      Error *local_err = NULL;
>      int thread_count, ret = 0;
>      uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
> +    /* We need one extra place for the packet header */
> +    uint32_t iov_count = 1;
>      uint8_t i;
>  
>      if (!migrate_multifd()) {
> @@ -1012,6 +1030,7 @@ bool multifd_send_setup(void)
>      qemu_sem_init(&multifd_send_state->channels_ready, 0);
>      qatomic_set(&multifd_send_state->exiting, 0);
>      multifd_send_state->ops = multifd_ops[migrate_multifd_compression()];
> +    iov_count += multifd_send_state->ops->get_iov_count(page_count);
>  
>      for (i = 0; i < thread_count; i++) {
>          MultiFDSendParams *p = &multifd_send_state->params[i];
> @@ -1026,8 +1045,7 @@ bool multifd_send_setup(void)
>          p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
>          p->packet->version = cpu_to_be32(MULTIFD_VERSION);
>          p->name = g_strdup_printf("multifdsend_%d", i);
> -        /* We need one extra place for the packet header */
> -        p->iov = g_new0(struct iovec, page_count + 1);
> +        p->iov = g_new0(struct iovec, iov_count);
>          p->page_size = qemu_target_page_size();
>          p->page_count = page_count;
>          p->write_flags = 0;
> diff --git a/migration/multifd.h b/migration/multifd.h
> index 8a1cad0996..d82495c508 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -201,6 +201,8 @@ typedef struct {
>      void (*recv_cleanup)(MultiFDRecvParams *p);
>      /* Read all pages */
>      int (*recv_pages)(MultiFDRecvParams *p, Error **errp);
> +    /* Get the count of required IOVs */
> +    uint32_t (*get_iov_count)(uint32_t page_count);
>  } MultiFDMethods;
>  
>  void multifd_register_ops(int method, MultiFDMethods *ops);