* [PATCH] system/main: comment lock rationale
@ 2025-05-15 17:46 Pierrick Bouvier
2025-05-15 17:48 ` Pierrick Bouvier
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Pierrick Bouvier @ 2025-05-15 17:46 UTC (permalink / raw)
To: qemu-devel; +Cc: qemu-trivial, npiggin, Paolo Bonzini, Pierrick Bouvier
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
system/main.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/system/main.c b/system/main.c
index 1c022067349..b8f7157cc34 100644
--- a/system/main.c
+++ b/system/main.c
@@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main;
int main(int argc, char **argv)
{
qemu_init(argc, argv);
+
+ /*
+ * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when
+ * initializing cpus, to block associated threads until initialization is
+ * complete. Replay_mutex lock is acquired on initialization, because it
+ * must be held when configuring icount_mode.
+ *
+ * On MacOS, qemu main event loop runs in a background thread, as main
+ * thread must be reserved for UI. Thus, we need to transfer lock ownership,
+ * and the simplest way to do that is to release them, and reacquire them
+ * from qemu_default_main.
+ */
bql_unlock();
replay_mutex_unlock();
+
if (qemu_main) {
QemuThread main_loop_thread;
qemu_thread_create(&main_loop_thread, "qemu_main",
--
2.47.2
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] system/main: comment lock rationale
2025-05-15 17:46 [PATCH] system/main: comment lock rationale Pierrick Bouvier
@ 2025-05-15 17:48 ` Pierrick Bouvier
2025-05-24 12:45 ` Richard Henderson
2025-05-27 8:55 ` Richard Henderson
2 siblings, 0 replies; 6+ messages in thread
From: Pierrick Bouvier @ 2025-05-15 17:48 UTC (permalink / raw)
To: qemu-devel; +Cc: qemu-trivial, npiggin, Paolo Bonzini
On 5/15/25 10:46 AM, Pierrick Bouvier wrote:
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
> system/main.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/system/main.c b/system/main.c
> index 1c022067349..b8f7157cc34 100644
> --- a/system/main.c
> +++ b/system/main.c
> @@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main;
> int main(int argc, char **argv)
> {
> qemu_init(argc, argv);
> +
> + /*
> + * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when
> + * initializing cpus, to block associated threads until initialization is
> + * complete. Replay_mutex lock is acquired on initialization, because it
> + * must be held when configuring icount_mode.
> + *
> + * On MacOS, qemu main event loop runs in a background thread, as main
> + * thread must be reserved for UI. Thus, we need to transfer lock ownership,
> + * and the simplest way to do that is to release them, and reacquire them
> + * from qemu_default_main.
> + */
> bql_unlock();
> replay_mutex_unlock();
> +
> if (qemu_main) {
> QemuThread main_loop_thread;
> qemu_thread_create(&main_loop_thread, "qemu_main",
This was requested previously by Nicholas:
https://lore.kernel.org/qemu-devel/D97QJO5Z909K.368VVIBFA17TA@gmail.com/
I sent this patch to qemu-devel some time ago, but it was never reviewed
nor pulled, despite multiple pings, so I'm trying again with qemu-trivial.
Regards,
Pierrick
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] system/main: comment lock rationale
2025-05-15 17:46 [PATCH] system/main: comment lock rationale Pierrick Bouvier
2025-05-15 17:48 ` Pierrick Bouvier
@ 2025-05-24 12:45 ` Richard Henderson
2025-05-27 8:55 ` Richard Henderson
2 siblings, 0 replies; 6+ messages in thread
From: Richard Henderson @ 2025-05-24 12:45 UTC (permalink / raw)
To: qemu-devel
On 5/15/25 18:46, Pierrick Bouvier wrote:
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
> system/main.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/system/main.c b/system/main.c
> index 1c022067349..b8f7157cc34 100644
> --- a/system/main.c
> +++ b/system/main.c
> @@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main;
> int main(int argc, char **argv)
> {
> qemu_init(argc, argv);
> +
> + /*
> + * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when
> + * initializing cpus, to block associated threads until initialization is
> + * complete. Replay_mutex lock is acquired on initialization, because it
> + * must be held when configuring icount_mode.
> + *
> + * On MacOS, qemu main event loop runs in a background thread, as main
> + * thread must be reserved for UI. Thus, we need to transfer lock ownership,
> + * and the simplest way to do that is to release them, and reacquire them
> + * from qemu_default_main.
> + */
> bql_unlock();
> replay_mutex_unlock();
> +
> if (qemu_main) {
> QemuThread main_loop_thread;
> qemu_thread_create(&main_loop_thread, "qemu_main",
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
r~
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] system/main: comment lock rationale
2025-05-15 17:46 [PATCH] system/main: comment lock rationale Pierrick Bouvier
2025-05-15 17:48 ` Pierrick Bouvier
2025-05-24 12:45 ` Richard Henderson
@ 2025-05-27 8:55 ` Richard Henderson
2 siblings, 0 replies; 6+ messages in thread
From: Richard Henderson @ 2025-05-27 8:55 UTC (permalink / raw)
To: qemu-devel
On 5/15/25 18:46, Pierrick Bouvier wrote:
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
> system/main.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/system/main.c b/system/main.c
> index 1c022067349..b8f7157cc34 100644
> --- a/system/main.c
> +++ b/system/main.c
> @@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main;
> int main(int argc, char **argv)
> {
> qemu_init(argc, argv);
> +
> + /*
> + * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when
> + * initializing cpus, to block associated threads until initialization is
> + * complete. Replay_mutex lock is acquired on initialization, because it
> + * must be held when configuring icount_mode.
> + *
> + * On MacOS, qemu main event loop runs in a background thread, as main
> + * thread must be reserved for UI. Thus, we need to transfer lock ownership,
> + * and the simplest way to do that is to release them, and reacquire them
> + * from qemu_default_main.
> + */
> bql_unlock();
> replay_mutex_unlock();
> +
> if (qemu_main) {
> QemuThread main_loop_thread;
> qemu_thread_create(&main_loop_thread, "qemu_main",
Queued, thanks.
r~
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] system/main: comment lock rationale
@ 2025-04-16 18:52 Pierrick Bouvier
2025-04-28 19:33 ` Pierrick Bouvier
0 siblings, 1 reply; 6+ messages in thread
From: Pierrick Bouvier @ 2025-04-16 18:52 UTC (permalink / raw)
To: qemu-devel
Cc: philmd, Phil Dennis-Jordan, Paolo Bonzini, Nicholas Piggin,
Stefan Hajnoczi, Pierrick Bouvier
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
system/main.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/system/main.c b/system/main.c
index 1c022067349..b8f7157cc34 100644
--- a/system/main.c
+++ b/system/main.c
@@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main;
int main(int argc, char **argv)
{
qemu_init(argc, argv);
+
+ /*
+ * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when
+ * initializing cpus, to block associated threads until initialization is
+ * complete. Replay_mutex lock is acquired on initialization, because it
+ * must be held when configuring icount_mode.
+ *
+ * On MacOS, qemu main event loop runs in a background thread, as main
+ * thread must be reserved for UI. Thus, we need to transfer lock ownership,
+ * and the simplest way to do that is to release them, and reacquire them
+ * from qemu_default_main.
+ */
bql_unlock();
replay_mutex_unlock();
+
if (qemu_main) {
QemuThread main_loop_thread;
qemu_thread_create(&main_loop_thread, "qemu_main",
--
2.39.5
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] system/main: comment lock rationale
2025-04-16 18:52 Pierrick Bouvier
@ 2025-04-28 19:33 ` Pierrick Bouvier
0 siblings, 0 replies; 6+ messages in thread
From: Pierrick Bouvier @ 2025-04-28 19:33 UTC (permalink / raw)
To: qemu-devel
Cc: philmd, Phil Dennis-Jordan, Paolo Bonzini, Nicholas Piggin,
Stefan Hajnoczi
On 4/16/25 11:52 AM, Pierrick Bouvier wrote:
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
> system/main.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/system/main.c b/system/main.c
> index 1c022067349..b8f7157cc34 100644
> --- a/system/main.c
> +++ b/system/main.c
> @@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main;
> int main(int argc, char **argv)
> {
> qemu_init(argc, argv);
> +
> + /*
> + * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when
> + * initializing cpus, to block associated threads until initialization is
> + * complete. Replay_mutex lock is acquired on initialization, because it
> + * must be held when configuring icount_mode.
> + *
> + * On MacOS, qemu main event loop runs in a background thread, as main
> + * thread must be reserved for UI. Thus, we need to transfer lock ownership,
> + * and the simplest way to do that is to release them, and reacquire them
> + * from qemu_default_main.
> + */
> bql_unlock();
> replay_mutex_unlock();
> +
> if (qemu_main) {
> QemuThread main_loop_thread;
> qemu_thread_create(&main_loop_thread, "qemu_main",
Gentle ping on this patch.
@Nicholas: as you asked for this patch, would that be possible for you
to review it?
Regards,
Pierrick
^ permalink raw reply [flat|nested] 6+ messages in thread
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2025-05-15 17:46 [PATCH] system/main: comment lock rationale Pierrick Bouvier
2025-05-15 17:48 ` Pierrick Bouvier
2025-05-24 12:45 ` Richard Henderson
2025-05-27 8:55 ` Richard Henderson
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2025-04-28 19:33 ` Pierrick Bouvier
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