On Mon, Feb 12, 2024 at 11:45 AM Ross Lagerwall
<ross.lagerw...@citrix.com> wrote:
>
> A common pattern is seen where a timer fires, the callback does some
> work, then rearms the timer which implicitly calls qemu_notify_event().
>
> qemu_notify_event() is supposed to interrupt the main loop's poll() by
> calling qemu_bh_schedule(). In the case that this is being called from a
> main loop callback, the main loop is already not waiting on poll() and
> instead it means the main loop does an addition iteration with a timeout
> of 0 to handle the bottom half wakeup, before once again polling with
> the expected timeout value.
>
> Detect this situation by skipping the qemu_bh_schedule() call if the
> default main context is currently owned by the caller. i.e. it is being
> called as part of a poll / timer callback. Adjust the scope of the main
> context acquire / release to cover the timer callbacks in
> qemu_clock_run_all_timers().
>
> Signed-off-by: Ross Lagerwall <ross.lagerw...@citrix.com>
> ---
> util/main-loop.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/util/main-loop.c b/util/main-loop.c
> index a0386cfeb60c..a2afbb7d0e13 100644
> --- a/util/main-loop.c
> +++ b/util/main-loop.c
> @@ -145,10 +145,16 @@ AioContext *qemu_get_aio_context(void)
>
> void qemu_notify_event(void)
> {
> + GMainContext *context;
> +
> if (!qemu_aio_context) {
> return;
> }
> - qemu_bh_schedule(qemu_notify_bh);
> +
> + context = g_main_context_default();
> + if (!g_main_context_is_owner(context)) {
> + qemu_bh_schedule(qemu_notify_bh);
> + }
> }
>
> static GArray *gpollfds;
> @@ -292,11 +298,8 @@ static void glib_pollfds_poll(void)
>
> static int os_host_main_loop_wait(int64_t timeout)
> {
> - GMainContext *context = g_main_context_default();
> int ret;
>
> - g_main_context_acquire(context);
> -
> glib_pollfds_fill(&timeout);
>
> bql_unlock();
> @@ -309,8 +312,6 @@ static int os_host_main_loop_wait(int64_t timeout)
>
> glib_pollfds_poll();
>
> - g_main_context_release(context);
> -
> return ret;
> }
> #else
> @@ -470,15 +471,12 @@ static int os_host_main_loop_wait(int64_t timeout)
> fd_set rfds, wfds, xfds;
> int nfds;
>
> - g_main_context_acquire(context);
> -
> /* XXX: need to suppress polling by better using win32 events */
> ret = 0;
> for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
> ret |= pe->func(pe->opaque);
> }
> if (ret != 0) {
> - g_main_context_release(context);
> return ret;
> }
>
> @@ -538,8 +536,6 @@ static int os_host_main_loop_wait(int64_t timeout)
> g_main_context_dispatch(context);
> }
>
> - g_main_context_release(context);
> -
> return select_ret || g_poll_ret;
> }
> #endif
> @@ -559,6 +555,7 @@ void main_loop_poll_remove_notifier(Notifier *notify)
>
> void main_loop_wait(int nonblocking)
> {
> + GMainContext *context = g_main_context_default();
> MainLoopPoll mlpoll = {
> .state = MAIN_LOOP_POLL_FILL,
> .timeout = UINT32_MAX,
> @@ -586,7 +583,10 @@ void main_loop_wait(int nonblocking)
> timerlistgroup_deadline_ns(
> &main_loop_tlg));
>
> + g_main_context_acquire(context);
> +
> ret = os_host_main_loop_wait(timeout_ns);
> +
> mlpoll.state = ret < 0 ? MAIN_LOOP_POLL_ERR : MAIN_LOOP_POLL_OK;
> notifier_list_notify(&main_loop_poll_notifiers, &mlpoll);
>
> @@ -598,6 +598,8 @@ void main_loop_wait(int nonblocking)
> icount_start_warp_timer();
> }
> qemu_clock_run_all_timers();
> +
> + g_main_context_release(context);
> }
>
> /* Functions to operate on the main QEMU AioContext. */
> --
> 2.43.0
>
Ping?
Ross
