debian/patches/extra/0006-migration-states-workaround-snapshot-performance-reg.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Fiona Ebner <f.ebner@proxmox.com>
   3 Date: Thu, 28 Sep 2023 11:19:14 +0200
   4 Subject: [PATCH] migration states: workaround snapshot performance regression
   5
   6 Commit 813cd616 ("migration: Use migration_transferred_bytes() to
   7 calculate rate_limit") introduced a prohibitive performance regression
   8 when taking a snapshot [0]. The reason turns out to be the flushing
   9 done by migration_transferred_bytes()
  10
  11 Just use a _noflush version of the relevant function as a workaround
  12 until upstream fixes the issue. This is inspired by a not-applied
  13 upstream series [1], but doing the very minimum to avoid the
  14 regression.
  15
  16 [0]: https://gitlab.com/qemu-project/qemu/-/issues/1821
  17 [1]: https://lists.nongnu.org/archive/html/qemu-devel/2023-05/msg07708.html
  18
  19 Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
  20 ---
  21  migration/migration-stats.c | 16 +++++++++++++++-
  22  1 file changed, 15 insertions(+), 1 deletion(-)
  23
  24 diff --git a/migration/migration-stats.c b/migration/migration-stats.c
  25 index 095d6d75bb..8073c8ebaa 100644
  26 --- a/migration/migration-stats.c
  27 +++ b/migration/migration-stats.c
  28 @@ -18,6 +18,20 @@
  29
  30  MigrationAtomicStats mig_stats;
  31
  32 +/*
  33 + * Same as migration_transferred_bytes below, but using the _noflush
  34 + * variant of qemu_file_transferred() to avoid a performance
  35 + * regression in migration_rate_exceeded().
  36 + */
  37 +static uint64_t migration_transferred_bytes_noflush(QEMUFile *f)
  38 +{
  39 +    uint64_t multifd = stat64_get(&mig_stats.multifd_bytes);
  40 +    uint64_t qemu_file = qemu_file_transferred_noflush(f);
  41 +
  42 +    trace_migration_transferred_bytes(qemu_file, multifd);
  43 +    return qemu_file + multifd;
  44 +}
  45 +
  46  bool migration_rate_exceeded(QEMUFile *f)
  47  {
  48      if (qemu_file_get_error(f)) {
  49 @@ -25,7 +39,7 @@ bool migration_rate_exceeded(QEMUFile *f)
  50      }
  51
  52      uint64_t rate_limit_start = stat64_get(&mig_stats.rate_limit_start);
  53 -    uint64_t rate_limit_current = migration_transferred_bytes(f);
  54 +    uint64_t rate_limit_current = migration_transferred_bytes_noflush(f);
  55      uint64_t rate_limit_used = rate_limit_current - rate_limit_start;
  56      uint64_t rate_limit_max = stat64_get(&mig_stats.rate_limit_max);
  57