From d9190117f3c701380701d6e9b2aa3c2446b9708f Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Mon, 1 May 2023 13:34:43 -0400 Subject: [PATCH 01/21] block: compile out assert_bdrv_graph_readable() by default RH-Author: Kevin Wolf RH-MergeRequest: 166: block/graph-lock: Disable locking for now RH-Bugzilla: 2186725 RH-Acked-by: Eric Blake RH-Acked-by: Emanuele Giuseppe Esposito RH-Acked-by: Stefan Hajnoczi RH-Commit: [1/4] d8cb4bb832c85e8216d97e57679a34c7bc6a8f71 (kmwolf/centos-qemu-kvm) 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 Message-Id: <20230501173443.153062-1-stefanha@redhat.com> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf (cherry picked from commit 58a2e3f5c37be02dac3086b81bdda9414b931edf) Signed-off-by: Kevin Wolf --- block/graph-lock.c | 3 +++ configure | 1 + meson.build | 2 ++ meson_options.txt | 2 ++ scripts/meson-buildoptions.sh | 4 ++++ 5 files changed, 12 insertions(+) diff --git a/block/graph-lock.c b/block/graph-lock.c index 454c31e691..259a7a0bde 100644 --- a/block/graph-lock.c +++ b/block/graph-lock.c @@ -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) diff --git a/configure b/configure index 800b5850f4..a62a3e6be9 100755 --- a/configure +++ b/configure @@ -806,6 +806,7 @@ 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" diff --git a/meson.build b/meson.build index c44d05a13f..d964e741e7 100644 --- a/meson.build +++ b/meson.build @@ -1956,6 +1956,7 @@ 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')) @@ -3833,6 +3834,7 @@ 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')} diff --git a/meson_options.txt b/meson_options.txt index fc9447d267..bc857fe68b 100644 --- a/meson_options.txt +++ b/meson_options.txt @@ -311,6 +311,8 @@ 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, diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh index 009fab1515..30e1f25259 100644 --- a/scripts/meson-buildoptions.sh +++ b/scripts/meson-buildoptions.sh @@ -21,6 +21,8 @@ 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' @@ -249,6 +251,8 @@ _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 ;; -- 2.39.3