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block: compile out assert_bdrv_graph_readable() by default

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reader_count() is a performance bottleneck because the global
aio_context_list_lock mutex causes thread contention. Put this debugging
assertion behind a new ./configure --enable-debug-graph-lock option and
disable it by default.

The --enable-debug-graph-lock option is also enabled by the more general
--enable-debug option.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230501173443.153062-1-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-05-01 13:34:43 -04:00 committed by Kevin Wolf
parent e19b157f3c
commit 58a2e3f5c3
5 changed files with 12 additions and 0 deletions
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3
block/graph-lock.c
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@ -265,7 +265,10 @@ void bdrv_graph_rdunlock_main_loop(void)
void assert_bdrv_graph_readable(void)
{
/* reader_count() is slow due to aio_context_list_lock lock contention */
#ifdef CONFIG_DEBUG_GRAPH_LOCK
assert(qemu_in_main_thread() || reader_count());
#endif
}
void assert_bdrv_graph_writable(void)

1
configure vendored
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@ -816,6 +816,7 @@ for opt do
--enable-debug)
# Enable debugging options that aren't excessively noisy
debug_tcg="yes"
meson_option_parse --enable-debug-graph-lock ""
meson_option_parse --enable-debug-mutex ""
meson_option_add -Doptimization=0
fortify_source="no"

2
meson.build
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@ -1963,6 +1963,7 @@ if get_option('debug_stack_usage') and have_coroutine_pool
have_coroutine_pool = false
endif
config_host_data.set10('CONFIG_COROUTINE_POOL', have_coroutine_pool)
config_host_data.set('CONFIG_DEBUG_GRAPH_LOCK', get_option('debug_graph_lock'))
config_host_data.set('CONFIG_DEBUG_MUTEX', get_option('debug_mutex'))
config_host_data.set('CONFIG_DEBUG_STACK_USAGE', get_option('debug_stack_usage'))
config_host_data.set('CONFIG_GPROF', get_option('gprof'))
@ -3841,6 +3842,7 @@ summary_info += {'PIE': get_option('b_pie')}
summary_info += {'static build': config_host.has_key('CONFIG_STATIC')}
summary_info += {'malloc trim support': has_malloc_trim}
summary_info += {'membarrier': have_membarrier}
summary_info += {'debug graph lock': get_option('debug_graph_lock')}
summary_info += {'debug stack usage': get_option('debug_stack_usage')}
summary_info += {'mutex debugging': get_option('debug_mutex')}
summary_info += {'memory allocator': get_option('malloc')}

2
meson_options.txt
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@ -319,6 +319,8 @@ option('rng_none', type: 'boolean', value: false,
description: 'dummy RNG, avoid using /dev/(u)random and getrandom()')
option('coroutine_pool', type: 'boolean', value: true,
description: 'coroutine freelist (better performance)')
option('debug_graph_lock', type: 'boolean', value: false,
description: 'graph lock debugging support')
option('debug_mutex', type: 'boolean', value: false,
description: 'mutex debugging support')
option('debug_stack_usage', type: 'boolean', value: false,

4
scripts/meson-buildoptions.sh
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@ -23,6 +23,8 @@ meson_options_help() {
printf "%s\n" ' QEMU'
printf "%s\n" ' --enable-cfi Control-Flow Integrity (CFI)'
printf "%s\n" ' --enable-cfi-debug Verbose errors in case of CFI violation'
printf "%s\n" ' --enable-debug-graph-lock'
printf "%s\n" ' graph lock debugging support'
printf "%s\n" ' --enable-debug-mutex mutex debugging support'
printf "%s\n" ' --enable-debug-stack-usage'
printf "%s\n" ' measure coroutine stack usage'
@ -254,6 +256,8 @@ _meson_option_parse() {
--datadir=*) quote_sh "-Ddatadir=$2" ;;
--enable-dbus-display) printf "%s" -Ddbus_display=enabled ;;
--disable-dbus-display) printf "%s" -Ddbus_display=disabled ;;
--enable-debug-graph-lock) printf "%s" -Ddebug_graph_lock=true ;;
--disable-debug-graph-lock) printf "%s" -Ddebug_graph_lock=false ;;
--enable-debug-mutex) printf "%s" -Ddebug_mutex=true ;;
--disable-debug-mutex) printf "%s" -Ddebug_mutex=false ;;
--enable-debug-stack-usage) printf "%s" -Ddebug_stack_usage=true ;;