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

[Liu, Yuan1]

> -----Original Message-----
> From: Fabiano Rosas <farosas@suse.de>
> Sent: Wednesday, March 6, 2024 4:24 AM
> To: Liu, Yuan1 <yuan1.liu@intel.com>; peterx@redhat.com
> Cc: qemu-devel@nongnu.org; hao.xiang@bytedance.com;
> bryan.zhang@bytedance.com; Liu, Yuan1 <yuan1.liu@intel.com>; Zou, Nanhai
> <nanhai.zou@intel.com>
> Subject: Re: [PATCH v4 2/8] migration/multifd: add get_iov_count in the
> multifd method
> 
> 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().

Yes, this is a good way, I will implement it in the next version

> >
> > 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);