Re: [PATCH v2 05/16] migration: Move rate_limit_max and rate_limit_used to migration_stats

[Leonardo Brás]

On Mon, 2023-05-15 at 21:56 +0200, Juan Quintela wrote:
> These way we can make them atomic and use this functions from any
> place.  I also moved all functions that use rate_limit to
> migration-stats.
> 
> Functions got renamed, they are not qemu_file anymore.
> 
> qemu_file_rate_limit -> migration_rate_exceeded
> qemu_file_set_rate_limit -> migration_rate_set
> qemu_file_get_rate_limit -> migration_rate_get
> qemu_file_reset_rate_limit -> migration_rate_reset
> qemu_file_acct_rate_limit -> migration_rate_account.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> 
> ---
> 
> s/this/these/ (harsh)
> If you have any good suggestion for better names, I am all ears.
> Fix missing / XFER_LIMIT_RATIO in migration_rate_set(quintela)
> ---
>  include/migration/qemu-file-types.h | 12 ++++++-
>  migration/migration-stats.h         | 47 ++++++++++++++++++++++++++
>  migration/options.h                 |  7 ----
>  migration/qemu-file.h               | 11 ------
>  hw/ppc/spapr.c                      |  4 +--
>  hw/s390x/s390-stattrib.c            |  2 +-
>  migration/block-dirty-bitmap.c      |  2 +-
>  migration/block.c                   |  5 +--
>  migration/migration-stats.c         | 44 ++++++++++++++++++++++++
>  migration/migration.c               | 14 ++++----
>  migration/multifd.c                 |  2 +-
>  migration/options.c                 |  7 ++--
>  migration/qemu-file.c               | 52 ++---------------------------
>  migration/ram.c                     |  2 +-
>  migration/savevm.c                  |  2 +-
>  15 files changed, 124 insertions(+), 89 deletions(-)
> 
> diff --git a/include/migration/qemu-file-types.h 
> b/include/migration/qemu-file-types.h
> index 1436f9ce92..9ba163f333 100644
> --- a/include/migration/qemu-file-types.h
> +++ b/include/migration/qemu-file-types.h
> @@ -165,6 +165,16 @@ size_t coroutine_mixed_fn 
> qemu_get_counted_string(QEMUFile *f, char buf[256]);
>  
>  void qemu_put_counted_string(QEMUFile *f, const char *name);
>  
> -int qemu_file_rate_limit(QEMUFile *f);
> +/**
> + * migration_rate_exceeded: Check if we have exceeded rate for this interval
> + *
> + * Checks if we have already transferred more data that we are allowed
> + * in the current interval.
> + *
> + * @f: QEMUFile used for main migration channel
> + *
> + * Returns if we should stop sending data for this interval.
> + */
> +bool migration_rate_exceeded(QEMUFile *f);
>  
>  #endif
> diff --git a/migration/migration-stats.h b/migration/migration-stats.h
> index 21402af9e4..e39c083245 100644
> --- a/migration/migration-stats.h
> +++ b/migration/migration-stats.h
> @@ -15,6 +15,12 @@
>  
>  #include "qemu/stats64.h"
>  
> +/*
> + * Amount of time to allocate to each "chunk" of bandwidth-throttled
> + * data.
> + */
> +#define BUFFER_DELAY     100
> +
>  /*
>   * If rate_limit_max is 0, there is special code to remove the rate
>   * limit.
> @@ -75,6 +81,14 @@ typedef struct {
>       * Number of bytes sent during precopy stage.
>       */
>      Stat64 precopy_bytes;
> +    /*
> +     * Maximum amount of data we can send in a cycle.
> +     */
> +    Stat64 rate_limit_max;
> +    /*
> +     * Amount of data we have sent in the current cycle.
> +     */
> +    Stat64 rate_limit_used;
>      /*
>       * How long has the setup stage took.
>       */
> @@ -100,4 +114,37 @@ extern MigrationAtomicStats mig_stats;
>   * Returns: Nothing.  The time is stored in val.
>   */
>  void migration_time_since(MigrationAtomicStats *stats, int64_t since);
> +
> +/**
> + * migration_rate_account: Increase the number of bytes transferred.
> + *
> + * Report on a number of bytes the have been transferred that need to
> + * be applied to the rate limiting calcuations.

s/calcuations/calculations

> + *
> + * @len: amount of bytes transferred
> + */
> +void migration_rate_account(uint64_t len);
> +
> +/**
> + * migration_rate_get: Get the maximum amount that can be transferred.
> + *
> + * Returns the maximum number of bytes that can be transferred in a cycle.
> + */
> +uint64_t migration_rate_get(void);

maybe migration_max_rate_get() ?

> +
> +/**
> + * migration_rate_reset: Reset the rate limit counter.
> + *
> + * This is called when we know we start a new transfer cycle.
> + */
> +void migration_rate_reset(void);
> +
> +/**
> + * migration_rate_set: Set the maximum amount that can be transferred.
> + *
> + * Sets the maximum amount of bytes that can be transferred in one cycle.
> + *
> + * @new_rate: new maximum amount
> + */
> +void migration_rate_set(uint64_t new_rate);

maybe migration_max_rate_set() ?

>  #endif
> diff --git a/migration/options.h b/migration/options.h
> index 5cca3326d6..45991af3c2 100644
> --- a/migration/options.h
> +++ b/migration/options.h
> @@ -17,13 +17,6 @@
>  #include "hw/qdev-properties.h"
>  #include "hw/qdev-properties-system.h"
>  
> -/* constants */
> -
> -/* Amount of time to allocate to each "chunk" of bandwidth-throttled
> - * data. */
> -#define BUFFER_DELAY     100
> -#define XFER_LIMIT_RATIO (1000 / BUFFER_DELAY)
> -
>  /* migration properties */
>  
>  extern Property migration_properties[];
> diff --git a/migration/qemu-file.h b/migration/qemu-file.h
> index bcc39081f2..e649718492 100644
> --- a/migration/qemu-file.h
> +++ b/migration/qemu-file.h
> @@ -130,17 +130,6 @@ void qemu_file_skip(QEMUFile *f, int size);
>   * accounting information tracks the total migration traffic.
>   */
>  void qemu_file_credit_transfer(QEMUFile *f, size_t size);
> -void qemu_file_reset_rate_limit(QEMUFile *f);
> -/*
> - * qemu_file_acct_rate_limit:
> - *
> - * Report on a number of bytes the have been transferred
> - * out of band from the main file object I/O methods, and
> - * need to be applied to the rate limiting calcuations
> - */
> -void qemu_file_acct_rate_limit(QEMUFile *f, uint64_t len);
> -void qemu_file_set_rate_limit(QEMUFile *f, uint64_t new_rate);
> -uint64_t qemu_file_get_rate_limit(QEMUFile *f);
>  int qemu_file_get_error_obj(QEMUFile *f, Error **errp);
>  int qemu_file_get_error_obj_any(QEMUFile *f1, QEMUFile *f2, Error **errp);
>  void qemu_file_set_error_obj(QEMUFile *f, int ret, Error *err);
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index ddc9c7b1a1..1baea16c96 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2166,7 +2166,7 @@ static void htab_save_first_pass(QEMUFile *f, 
> SpaprMachineState *spapr,
>                  break;
>              }
>          }
> -    } while ((index < htabslots) && !qemu_file_rate_limit(f));
> +    } while ((index < htabslots) && !migration_rate_exceeded(f));
>  
>      if (index >= htabslots) {
>          assert(index == htabslots);
> @@ -2237,7 +2237,7 @@ static int htab_save_later_pass(QEMUFile *f, 
> SpaprMachineState *spapr,
>              assert(index == htabslots);
>              index = 0;
>          }
> -    } while ((examined < htabslots) && (!qemu_file_rate_limit(f) || final));
> +    } while ((examined < htabslots) && (!migration_rate_exceeded(f) || 
> final));
>  
>      if (index >= htabslots) {
>          assert(index == htabslots);
> diff --git a/hw/s390x/s390-stattrib.c b/hw/s390x/s390-stattrib.c
> index aed919ad7d..220e845d12 100644
> --- a/hw/s390x/s390-stattrib.c
> +++ b/hw/s390x/s390-stattrib.c
> @@ -209,7 +209,7 @@ static int cmma_save(QEMUFile *f, void *opaque, int final)
>          return -ENOMEM;
>      }
>  
> -    while (final ? 1 : qemu_file_rate_limit(f) == 0) {
> +    while (final ? 1 : migration_rate_exceeded(f) == 0) {
>          reallen = sac->get_stattr(sas, &start_gfn, buflen, buf);
>          if (reallen < 0) {
>              g_free(buf);
> diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
> index 20f36e6bd8..032fc5f405 100644
> --- a/migration/block-dirty-bitmap.c
> +++ b/migration/block-dirty-bitmap.c
> @@ -706,7 +706,7 @@ static void bulk_phase(QEMUFile *f, DBMSaveState *s, bool 
> limit)
>      QSIMPLEQ_FOREACH(dbms, &s->dbms_list, entry) {
>          while (!dbms->bulk_completed) {
>              bulk_phase_send_chunk(f, s, dbms);
> -            if (limit && qemu_file_rate_limit(f)) {
> +            if (limit && migration_rate_exceeded(f)) {
>                  return;
>              }
>          }
> diff --git a/migration/block.c b/migration/block.c
> index 12617b4152..b9580a6c7e 100644
> --- a/migration/block.c
> +++ b/migration/block.c
> @@ -23,6 +23,7 @@
>  #include "block/dirty-bitmap.h"
>  #include "migration/misc.h"
>  #include "migration.h"
> +#include "migration-stats.h"
>  #include "migration/register.h"
>  #include "qemu-file.h"
>  #include "migration/vmstate.h"
> @@ -625,7 +626,7 @@ static int flush_blks(QEMUFile *f)
>  
>      blk_mig_lock();
>      while ((blk = QSIMPLEQ_FIRST(&block_mig_state.blk_list)) != NULL) {
> -        if (qemu_file_rate_limit(f)) {
> +        if (migration_rate_exceeded(f)) {
>              break;
>          }
>          if (blk->ret < 0) {
> @@ -762,7 +763,7 @@ static int block_save_iterate(QEMUFile *f, void *opaque)
>      /* control the rate of transfer */
>      blk_mig_lock();
>      while (block_mig_state.read_done * BLK_MIG_BLOCK_SIZE <
> -           qemu_file_get_rate_limit(f) &&
> +           migration_rate_get() &&
>             block_mig_state.submitted < MAX_PARALLEL_IO &&
>             (block_mig_state.submitted + block_mig_state.read_done) <
>             MAX_IO_BUFFERS) {
> diff --git a/migration/migration-stats.c b/migration/migration-stats.c
> index 3431453c90..1b16edae7d 100644
> --- a/migration/migration-stats.c
> +++ b/migration/migration-stats.c
> @@ -13,6 +13,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/stats64.h"
>  #include "qemu/timer.h"
> +#include "qemu-file.h"
>  #include "migration-stats.h"
>  
>  MigrationAtomicStats mig_stats;
> @@ -22,3 +23,46 @@ void migration_time_since(MigrationAtomicStats *stats, 
> int64_t since)
>      int64_t now = qemu_clock_get_ms(QEMU_CLOCK_HOST);
>      stat64_set(&stats->setup_time, now - since);
>  }
> +
> +bool migration_rate_exceeded(QEMUFile *f)

Really liked this name, and how it fits the usage :)

> +{
> +    if (qemu_file_get_error(f)) {
> +        return true;
> +    }
> +
> +    uint64_t rate_limit_used = stat64_get(&mig_stats.rate_limit_used);
> +    uint64_t rate_limit_max = stat64_get(&mig_stats.rate_limit_max);
> +
> +    if (rate_limit_max == RATE_LIMIT_MAX) {
> +        return false;
> +    }
> +    if (rate_limit_max > 0 && rate_limit_used > rate_limit_max) {
> +        return true;
> +    }
> +    return false;
> +}
> +
> +uint64_t migration_rate_get(void)
> +{
> +    return stat64_get(&mig_stats.rate_limit_max);
> +}
> +
> +#define XFER_LIMIT_RATIO (1000 / BUFFER_DELAY)
> +
> +void migration_rate_set(uint64_t limit)
> +{
> +    /*
> +     * 'limit' is per second.  But we check it each BUFER_DELAY miliseconds.
> +     */
> +    stat64_set(&mig_stats.rate_limit_max, limit / XFER_LIMIT_RATIO);
> +}
> +
> +void migration_rate_reset(void)
> +{
> +    stat64_set(&mig_stats.rate_limit_used, 0);
> +}
> +
> +void migration_rate_account(uint64_t len)
> +{
> +    stat64_add(&mig_stats.rate_limit_used, len);
> +}
> diff --git a/migration/migration.c b/migration/migration.c
> index e9466273bb..594709dbbc 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -2119,7 +2119,7 @@ static int postcopy_start(MigrationState *ms)
>       * will notice we're in POSTCOPY_ACTIVE and not actually
>       * wrap their state up here
>       */
> -    qemu_file_set_rate_limit(ms->to_dst_file, bandwidth);
> +    migration_rate_set(bandwidth);
>      if (migrate_postcopy_ram()) {
>          /* Ping just for debugging, helps line traces up */
>          qemu_savevm_send_ping(ms->to_dst_file, 2);
> @@ -2303,7 +2303,7 @@ static void migration_completion(MigrationState *s)
>                   * them if migration fails or is cancelled.
>                   */
>                  s->block_inactive = !migrate_colo();
> -                qemu_file_set_rate_limit(s->to_dst_file, RATE_LIMIT_MAX);
> +                migration_rate_set(RATE_LIMIT_MAX);
>                  ret = qemu_savevm_state_complete_precopy(s->to_dst_file, 
> false,
>                                                           s->block_inactive);
>              }
> @@ -2698,7 +2698,7 @@ static void migration_update_counters(MigrationState *s,
>              stat64_get(&mig_stats.dirty_bytes_last_sync) / bandwidth;
>      }
>  
> -    qemu_file_reset_rate_limit(s->to_dst_file);
> +    migration_rate_reset();
>  
>      update_iteration_initial_status(s);
>  
> @@ -2851,7 +2851,7 @@ bool migration_rate_limit(void)
>  
>      bool urgent = false;
>      migration_update_counters(s, now);
> -    if (qemu_file_rate_limit(s->to_dst_file)) {
> +    if (migration_rate_exceeded(s->to_dst_file)) {
>  
>          if (qemu_file_get_error(s->to_dst_file)) {
>              return false;
> @@ -2973,7 +2973,7 @@ static void *migration_thread(void *opaque)
>      trace_migration_thread_setup_complete();
>  
>      while (migration_is_active(s)) {
> -        if (urgent || !qemu_file_rate_limit(s->to_dst_file)) {
> +        if (urgent || !migration_rate_exceeded(s->to_dst_file)) {
>              MigIterateState iter_state = migration_iteration_run(s);
>              if (iter_state == MIG_ITERATE_SKIP) {
>                  continue;
> @@ -3047,7 +3047,7 @@ static void *bg_migration_thread(void *opaque)
>      rcu_register_thread();
>      object_ref(OBJECT(s));
>  
> -    qemu_file_set_rate_limit(s->to_dst_file, RATE_LIMIT_MAX);
> +    migration_rate_set(RATE_LIMIT_MAX);
>  
>      setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
>      /*
> @@ -3219,7 +3219,7 @@ void migrate_fd_connect(MigrationState *s, Error 
> *error_in)
>          notifier_list_notify(&migration_state_notifiers, s);
>      }
>  
> -    qemu_file_set_rate_limit(s->to_dst_file, rate_limit);
> +    migration_rate_set(rate_limit);
>      qemu_file_set_blocking(s->to_dst_file, true);
>  
>      /*
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 5c4298eadf..5052091ce2 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -431,7 +431,7 @@ static int multifd_send_pages(QEMUFile *f)
>      multifd_send_state->pages = p->pages;
>      p->pages = pages;
>      transferred = ((uint64_t) pages->num) * p->page_size + p->packet_len;
> -    qemu_file_acct_rate_limit(f, transferred);
> +    migration_rate_account(transferred);
>      qemu_mutex_unlock(&p->mutex);
>      stat64_add(&mig_stats.transferred, transferred);
>      stat64_add(&mig_stats.multifd_bytes, transferred);
> diff --git a/migration/options.c b/migration/options.c
> index c2a278ee2d..b62ab30cd5 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -23,6 +23,7 @@
>  #include "migration/colo.h"
>  #include "migration/misc.h"
>  #include "migration.h"
> +#include "migration-stats.h"
>  #include "qemu-file.h"
>  #include "ram.h"
>  #include "options.h"
> @@ -1242,8 +1243,7 @@ static void migrate_params_apply(MigrateSetParameters 
> *params, Error **errp)
>      if (params->has_max_bandwidth) {
>          s->parameters.max_bandwidth = params->max_bandwidth;
>          if (s->to_dst_file && !migration_in_postcopy()) {
> -            qemu_file_set_rate_limit(s->to_dst_file,
> -                                s->parameters.max_bandwidth);
> +            migration_rate_set(s->parameters.max_bandwidth);
>          }
>      }
>  
> @@ -1272,8 +1272,7 @@ static void migrate_params_apply(MigrateSetParameters 
> *params, Error **errp)
>      if (params->has_max_postcopy_bandwidth) {
>          s->parameters.max_postcopy_bandwidth = 
> params->max_postcopy_bandwidth;
>          if (s->to_dst_file && migration_in_postcopy()) {
> -            qemu_file_set_rate_limit(s->to_dst_file,
> -                    s->parameters.max_postcopy_bandwidth);
> +            migration_rate_set(s->parameters.max_postcopy_bandwidth);
>          }
>      }
>      if (params->has_max_cpu_throttle) {
> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index 956bd2a580..9c67b52fe0 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -41,17 +41,6 @@ struct QEMUFile {
>      QIOChannel *ioc;
>      bool is_writable;
>  
> -    /*
> -     * Maximum amount of data in bytes to transfer during one
> -     * rate limiting time window
> -     */
> -    uint64_t rate_limit_max;
> -    /*
> -     * Total amount of data in bytes queued for transfer
> -     * during this rate limiting time window
> -     */
> -    uint64_t rate_limit_used;
> -
>      /* The sum of bytes transferred on the wire */
>      uint64_t total_transferred;
>  
> @@ -303,7 +292,7 @@ void qemu_fflush(QEMUFile *f)
>              qemu_file_set_error_obj(f, -EIO, local_error);
>          } else {
>              uint64_t size = iov_size(f->iov, f->iovcnt);
> -            qemu_file_acct_rate_limit(f, size);
> +            migration_rate_account(size);
>              f->total_transferred += size;
>          }
>  
> @@ -356,7 +345,7 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t 
> block_offset,
>          int ret = f->hooks->save_page(f, block_offset,
>                                        offset, size, bytes_sent);
>          if (ret != RAM_SAVE_CONTROL_NOT_SUPP) {
> -            qemu_file_acct_rate_limit(f, size);
> +            migration_rate_account(size);
>          }
>  
>          if (ret != RAM_SAVE_CONTROL_DELAYED &&
> @@ -727,43 +716,6 @@ uint64_t qemu_file_transferred(QEMUFile *f)
>      return f->total_transferred;
>  }
>  
> -int qemu_file_rate_limit(QEMUFile *f)
> -{
> -    if (qemu_file_get_error(f)) {
> -        return 1;
> -    }
> -    if (f->rate_limit_max == RATE_LIMIT_MAX) {
> -        return 0;
> -    }
> -    if (f->rate_limit_used > f->rate_limit_max) {
> -        return 1;
> -    }
> -    return 0;
> -}
> -
> -uint64_t qemu_file_get_rate_limit(QEMUFile *f)
> -{
> -    return f->rate_limit_max;
> -}
> -
> -void qemu_file_set_rate_limit(QEMUFile *f, uint64_t limit)
> -{
> -    /*
> -     * 'limit' is per second.  But we check it each 100 miliseconds.
> -     */
> -    f->rate_limit_max = limit / XFER_LIMIT_RATIO;
> -}
> -
> -void qemu_file_reset_rate_limit(QEMUFile *f)
> -{
> -    f->rate_limit_used = 0;
> -}
> -
> -void qemu_file_acct_rate_limit(QEMUFile *f, uint64_t len)
> -{
> -    f->rate_limit_used += len;
> -}
> -
>  void qemu_put_be16(QEMUFile *f, unsigned int v)
>  {
>      qemu_put_byte(f, v >> 8);
> diff --git a/migration/ram.c b/migration/ram.c
> index fd5a8db0f8..a706edecc0 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -3126,7 +3126,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
>  
>          t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>          i = 0;
> -        while ((ret = qemu_file_rate_limit(f)) == 0 ||
> +        while ((ret = migration_rate_exceeded(f)) == 0 ||

migration_rate_exceeded() now returns bool, so it feels weird to compare it to
zero instead of false. 

Also, I noticed that after this ret is used in:
[...]
    if (ret >= 0
        && migration_is_setup_or_active(migrate_get_current()->state)) {
[...]

IIRC bool promotion to int will always be 0 or 1, and (ret >= 0) test will be
always true. Also, qemu_file_rate_limit() only returns 0 or 1, so either this
test is unnecessary, or this could be a bug, and (ret == 0) is the correct test.

If the test is unnecessary, it would be removed and we could have:

-        while ((ret = qemu_file_rate_limit(f)) == 0 ||
+        while (!migration_rate_exceeded(f) ||

(ret could be local to if (ret >= 0 ...) now)

If this is a bug, then an one-liner 'could' be:

-       while ((ret = qemu_file_rate_limit(f)) == 0 ||
+       while ((ret = migration_rate_exceeded(f) ? -1 : 0) == 0 ||

But I strongly advise on doing this instead:

#####
diff --git a/migration/ram.c b/migration/ram.c
index f69d8d42b0..1643dd564c 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3084,7 +3084,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
 {
     RAMState **temp = opaque;
     RAMState *rs = *temp;
-    int ret = 0;
+    bool rate_exceeded = false;
     int i;
     int64_t t0;
     int done = 0;
@@ -3116,7 +3116,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
 
         t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
         i = 0;
-        while ((ret = qemu_file_rate_limit(f)) == 0 ||
+        while (!(rate_exceeded = migration_rate_exceeded(f)) ||
                postcopy_has_request(rs)) {
             int pages;
 
@@ -3172,8 +3172,10 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
     ram_control_after_iterate(f, RAM_CONTROL_ROUND);
 
 out:
-    if (ret >= 0
+    if (!rate_exceeded
         && migration_is_setup_or_active(migrate_get_current()->state)) {
+        int ret;
+
         if (migrate_multifd_flush_after_each_section()) {
             ret = multifd_send_sync_main(rs-
>pss[RAM_CHANNEL_PRECOPY].pss_channel);
             if (ret < 0) {
@@ -3186,9 +3188,10 @@ out:
         ram_transferred_add(8);
 
         ret = qemu_file_get_error(f);
-    }
-    if (ret < 0) {
-        return ret;
+
+        if (ret < 0) {
+            return ret;
+        }
     }
 
     return done;

#####

Notice I moved the if(ret < 0) inside the if (rate_exceeded >= 0 ...), reason
being neither qemu_file_rate_limit() nor (int) rate_exceeded will ever be < 0.


>                 postcopy_has_request(rs)) {
>              int pages;
>  
> diff --git a/migration/savevm.c b/migration/savevm.c
> index c7af9050c2..6b783d9c39 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1345,7 +1345,7 @@ int qemu_savevm_state_iterate(QEMUFile *f, bool 
> postcopy)
>              !(se->ops->has_postcopy && se->ops->has_postcopy(se->opaque))) {
>              continue;
>          }
> -        if (qemu_file_rate_limit(f)) {
> +        if (migration_rate_exceeded(f)) {
>              return 0;
>          }
>          trace_savevm_section_start(se->idstr, se->section_id);

Other than that, it looks fine :)

Thanks!