| Message ID | 20240212114541.1440728-1-ross.lagerwall@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | main-loop: Avoid some unnecessary poll calls | expand |
On Mon, Feb 12, 2024 at 11:45 AM Ross Lagerwall <ross.lagerwall@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.lagerwall@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
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. */
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.lagerwall@citrix.com> --- util/main-loop.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-)