debian/patches/extra/0014-block-compile-out-assert_bdrv_graph_readable-by-defa.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Stefan Hajnoczi <stefanha@redhat.com>
   3 Date: Mon, 1 May 2023 13:34:43 -0400
   4 Subject: [PATCH] block: compile out assert_bdrv_graph_readable() by default
   5
   6 reader_count() is a performance bottleneck because the global
   7 aio_context_list_lock mutex causes thread contention. Put this debugging
   8 assertion behind a new ./configure --enable-debug-graph-lock option and
   9 disable it by default.
  10
  11 The --enable-debug-graph-lock option is also enabled by the more general
  12 --enable-debug option.
  13
  14 Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
  15 (picked up from https://lists.nongnu.org/archive/html/qemu-devel/2023-05/msg00058.html)
  16 Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
  17 ---
  18  block/graph-lock.c            | 3 +++
  19  configure                     | 1 +
  20  meson.build                   | 2 ++
  21  meson_options.txt             | 2 ++
  22  scripts/meson-buildoptions.sh | 4 ++++
  23  5 files changed, 12 insertions(+)
  24
  25 diff --git a/block/graph-lock.c b/block/graph-lock.c
  26 index 454c31e691..259a7a0bde 100644
  27 --- a/block/graph-lock.c
  28 +++ b/block/graph-lock.c
  29 @@ -265,7 +265,10 @@ void bdrv_graph_rdunlock_main_loop(void)
  30
  31  void assert_bdrv_graph_readable(void)
  32  {
  33 +    /* reader_count() is slow due to aio_context_list_lock lock contention */
  34 +#ifdef CONFIG_DEBUG_GRAPH_LOCK
  35      assert(qemu_in_main_thread() || reader_count());
  36 +#endif
  37  }
  38
  39  void assert_bdrv_graph_writable(void)
  40 diff --git a/configure b/configure
  41 index 800b5850f4..a62a3e6be9 100755
  42 --- a/configure
  43 +++ b/configure
  44 @@ -806,6 +806,7 @@ for opt do
  45    --enable-debug)
  46        # Enable debugging options that aren't excessively noisy
  47        debug_tcg="yes"
  48 +      meson_option_parse --enable-debug-graph-lock ""
  49        meson_option_parse --enable-debug-mutex ""
  50        meson_option_add -Doptimization=0
  51        fortify_source="no"
  52 diff --git a/meson.build b/meson.build
  53 index c44d05a13f..d964e741e7 100644
  54 --- a/meson.build
  55 +++ b/meson.build
  56 @@ -1956,6 +1956,7 @@ if get_option('debug_stack_usage') and have_coroutine_pool
  57    have_coroutine_pool = false
  58  endif
  59  config_host_data.set10('CONFIG_COROUTINE_POOL', have_coroutine_pool)
  60 +config_host_data.set('CONFIG_DEBUG_GRAPH_LOCK', get_option('debug_graph_lock'))
  61  config_host_data.set('CONFIG_DEBUG_MUTEX', get_option('debug_mutex'))
  62  config_host_data.set('CONFIG_DEBUG_STACK_USAGE', get_option('debug_stack_usage'))
  63  config_host_data.set('CONFIG_GPROF', get_option('gprof'))
  64 @@ -3833,6 +3834,7 @@ summary_info += {'PIE':               get_option('b_pie')}
  65  summary_info += {'static build':      config_host.has_key('CONFIG_STATIC')}
  66  summary_info += {'malloc trim support': has_malloc_trim}
  67  summary_info += {'membarrier':        have_membarrier}
  68 +summary_info += {'debug graph lock':  get_option('debug_graph_lock')}
  69  summary_info += {'debug stack usage': get_option('debug_stack_usage')}
  70  summary_info += {'mutex debugging':   get_option('debug_mutex')}
  71  summary_info += {'memory allocator':  get_option('malloc')}
  72 diff --git a/meson_options.txt b/meson_options.txt
  73 index fc9447d267..bc857fe68b 100644
  74 --- a/meson_options.txt
  75 +++ b/meson_options.txt
  76 @@ -311,6 +311,8 @@ option('rng_none', type: 'boolean', value: false,
  77         description: 'dummy RNG, avoid using /dev/(u)random and getrandom()')
  78  option('coroutine_pool', type: 'boolean', value: true,
  79         description: 'coroutine freelist (better performance)')
  80 +option('debug_graph_lock', type: 'boolean', value: false,
  81 +       description: 'graph lock debugging support')
  82  option('debug_mutex', type: 'boolean', value: false,
  83         description: 'mutex debugging support')
  84  option('debug_stack_usage', type: 'boolean', value: false,
  85 diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh
  86 index 009fab1515..30e1f25259 100644
  87 --- a/scripts/meson-buildoptions.sh
  88 +++ b/scripts/meson-buildoptions.sh
  89 @@ -21,6 +21,8 @@ meson_options_help() {
  90    printf "%s\n" '                           QEMU'
  91    printf "%s\n" '  --enable-cfi             Control-Flow Integrity (CFI)'
  92    printf "%s\n" '  --enable-cfi-debug       Verbose errors in case of CFI violation'
  93 +  printf "%s\n" '  --enable-debug-graph-lock'
  94 +  printf "%s\n" '                           graph lock debugging support'
  95    printf "%s\n" '  --enable-debug-mutex     mutex debugging support'
  96    printf "%s\n" '  --enable-debug-stack-usage'
  97    printf "%s\n" '                           measure coroutine stack usage'
  98 @@ -249,6 +251,8 @@ _meson_option_parse() {
  99      --datadir=*) quote_sh "-Ddatadir=$2" ;;
 100      --enable-dbus-display) printf "%s" -Ddbus_display=enabled ;;
 101      --disable-dbus-display) printf "%s" -Ddbus_display=disabled ;;
 102 +    --enable-debug-graph-lock) printf "%s" -Ddebug_graph_lock=true ;;
 103 +    --disable-debug-graph-lock) printf "%s" -Ddebug_graph_lock=false ;;
 104      --enable-debug-mutex) printf "%s" -Ddebug_mutex=true ;;
 105      --disable-debug-mutex) printf "%s" -Ddebug_mutex=false ;;
 106      --enable-debug-stack-usage) printf "%s" -Ddebug_stack_usage=true ;;