On Fri, 29 Aug 2025 17:31:14 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:
> There is no reason for some accelerators to use qemu_wait_io_event_common
> (which is separated from qemu_wait_io_event() specifically for round
> robin). They can also check for events directly on the first pass through
> the loop, instead of setting cpu->exit_request to true.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> ---
> accel/dummy-cpus.c | 2 +-
> accel/hvf/hvf-accel-ops.c | 2 +-
> accel/kvm/kvm-accel-ops.c | 3 ++-
> accel/tcg/tcg-accel-ops-mttcg.c | 7 ++---
> accel/tcg/tcg-accel-ops-rr.c | 43 ++++++++++++++-----------------
> target/i386/nvmm/nvmm-accel-ops.c | 6 ++---
> target/i386/whpx/whpx-accel-ops.c | 6 ++---
> 7 files changed, 30 insertions(+), 39 deletions(-)
>
> diff --git a/accel/dummy-cpus.c b/accel/dummy-cpus.c
> index 03cfc0fa01e..1f74c727c42 100644
> --- a/accel/dummy-cpus.c
> +++ b/accel/dummy-cpus.c
> @@ -43,6 +43,7 @@ static void *dummy_cpu_thread_fn(void *arg)
> qemu_guest_random_seed_thread_part2(cpu->random_seed);
>
> do {
> + qemu_wait_io_event(cpu);
> bql_unlock();
> #ifndef _WIN32
> do {
> @@ -57,7 +58,6 @@ static void *dummy_cpu_thread_fn(void *arg)
> qemu_sem_wait(&cpu->sem);
> #endif
> bql_lock();
> - qemu_wait_io_event(cpu);
> } while (!cpu->unplug);
>
> bql_unlock();
> diff --git a/accel/hvf/hvf-accel-ops.c b/accel/hvf/hvf-accel-ops.c
> index d488d6afbac..4ba3e40831f 100644
> --- a/accel/hvf/hvf-accel-ops.c
> +++ b/accel/hvf/hvf-accel-ops.c
> @@ -192,13 +192,13 @@ static void *hvf_cpu_thread_fn(void *arg)
> qemu_guest_random_seed_thread_part2(cpu->random_seed);
>
> do {
> + qemu_wait_io_event(cpu);
> if (cpu_can_run(cpu)) {
> r = hvf_vcpu_exec(cpu);
> if (r == EXCP_DEBUG) {
> cpu_handle_guest_debug(cpu);
> }
> }
> - qemu_wait_io_event(cpu);
> } while (!cpu->unplug || cpu_can_run(cpu));
>
> hvf_vcpu_destroy(cpu);
> diff --git a/accel/kvm/kvm-accel-ops.c b/accel/kvm/kvm-accel-ops.c
> index b709187c7d7..80f0141a8a6 100644
> --- a/accel/kvm/kvm-accel-ops.c
> +++ b/accel/kvm/kvm-accel-ops.c
> @@ -47,13 +47,14 @@ static void *kvm_vcpu_thread_fn(void *arg)
> qemu_guest_random_seed_thread_part2(cpu->random_seed);
>
> do {
> + qemu_wait_io_event(cpu);
> +
> if (cpu_can_run(cpu)) {
> r = kvm_cpu_exec(cpu);
> if (r == EXCP_DEBUG) {
> cpu_handle_guest_debug(cpu);
> }
> }
> - qemu_wait_io_event(cpu);
> } while (!cpu->unplug || cpu_can_run(cpu));
>
> kvm_destroy_vcpu(cpu);
> diff --git a/accel/tcg/tcg-accel-ops-mttcg.c b/accel/tcg/tcg-accel-ops-mttcg.c
> index 1148ebcaae5..04012900a30 100644
> --- a/accel/tcg/tcg-accel-ops-mttcg.c
> +++ b/accel/tcg/tcg-accel-ops-mttcg.c
> @@ -84,10 +84,9 @@ static void *mttcg_cpu_thread_fn(void *arg)
> cpu_thread_signal_created(cpu);
> qemu_guest_random_seed_thread_part2(cpu->random_seed);
>
> - /* process any pending work */
> - qatomic_set(&cpu->exit_request, true);
> -
> do {
> + qemu_wait_io_event(cpu);
> +
> if (cpu_can_run(cpu)) {
> int r;
> bql_unlock();
> @@ -112,8 +111,6 @@ static void *mttcg_cpu_thread_fn(void *arg)
> break;
> }
> }
> -
> - qemu_wait_io_event(cpu);
> } while (!cpu->unplug || cpu_can_run(cpu));
>
> tcg_cpu_destroy(cpu);
> diff --git a/accel/tcg/tcg-accel-ops-rr.c b/accel/tcg/tcg-accel-ops-rr.c
> index e9d291dc391..28897288db7 100644
> --- a/accel/tcg/tcg-accel-ops-rr.c
> +++ b/accel/tcg/tcg-accel-ops-rr.c
> @@ -211,13 +211,30 @@ static void *rr_cpu_thread_fn(void *arg)
>
> cpu = first_cpu;
>
> - /* process any pending work */
> - qatomic_set(&cpu->exit_request, true);
> -
> while (1) {
> /* Only used for icount_enabled() */
> int64_t cpu_budget = 0;
>
> + if (cpu) {
> + /*
> + * This could even reset exit_request for all CPUs, but in practice
> + * races between CPU exits and changes to "cpu" are so rare that
> + * there's no advantage in doing so.
> + */
> + qatomic_set(&cpu->exit_request, false);
> + }
> +
> + if (icount_enabled() && all_cpu_threads_idle()) {
> + /*
> + * When all cpus are sleeping (e.g in WFI), to avoid a deadlock
> + * in the main_loop, wake it up in order to start the warp timer.
> + */
> + qemu_notify_event();
> + }
> +
> + rr_wait_io_event();
> + rr_deal_with_unplugged_cpus();
> +
> bql_unlock();
> replay_mutex_lock();
> bql_lock();
> @@ -285,26 +302,6 @@ static void *rr_cpu_thread_fn(void *arg)
>
> /* Does not need a memory barrier because a spurious wakeup is okay. */
> qatomic_set(&rr_current_cpu, NULL);
> -
> - if (cpu) {
> - /*
> - * This could even reset exit_request for all CPUs, but in practice
> - * races between CPU exits and changes to "cpu" are so rare that
> - * there's no advantage in doing so.
> - */
> - qatomic_set(&cpu->exit_request, false);
> - }
> -
> - if (icount_enabled() && all_cpu_threads_idle()) {
> - /*
> - * When all cpus are sleeping (e.g in WFI), to avoid a deadlock
> - * in the main_loop, wake it up in order to start the warp timer.
> - */
> - qemu_notify_event();
> - }
> -
> - rr_wait_io_event();
> - rr_deal_with_unplugged_cpus();
> }
>
> g_assert_not_reached();
> diff --git a/target/i386/nvmm/nvmm-accel-ops.c b/target/i386/nvmm/nvmm-accel-ops.c
> index 86869f133e9..f51244740d8 100644
> --- a/target/i386/nvmm/nvmm-accel-ops.c
> +++ b/target/i386/nvmm/nvmm-accel-ops.c
> @@ -42,16 +42,14 @@ static void *qemu_nvmm_cpu_thread_fn(void *arg)
> qemu_guest_random_seed_thread_part2(cpu->random_seed);
>
> do {
> + qemu_wait_io_event(cpu);
> +
> if (cpu_can_run(cpu)) {
> r = nvmm_vcpu_exec(cpu);
> if (r == EXCP_DEBUG) {
> cpu_handle_guest_debug(cpu);
> }
> }
> - while (cpu_thread_is_idle(cpu)) {
> - qemu_cond_wait_bql(cpu->halt_cond);
> - }
> - qemu_wait_io_event_common(cpu);
> } while (!cpu->unplug || cpu_can_run(cpu));
>
> nvmm_destroy_vcpu(cpu);
> diff --git a/target/i386/whpx/whpx-accel-ops.c b/target/i386/whpx/whpx-accel-ops.c
> index da58805b1a6..611eeedeef7 100644
> --- a/target/i386/whpx/whpx-accel-ops.c
> +++ b/target/i386/whpx/whpx-accel-ops.c
> @@ -42,16 +42,14 @@ static void *whpx_cpu_thread_fn(void *arg)
> qemu_guest_random_seed_thread_part2(cpu->random_seed);
>
> do {
> + qemu_wait_io_event(cpu);
> +
> if (cpu_can_run(cpu)) {
> r = whpx_vcpu_exec(cpu);
> if (r == EXCP_DEBUG) {
> cpu_handle_guest_debug(cpu);
> }
> }
> - while (cpu_thread_is_idle(cpu)) {
> - qemu_cond_wait_bql(cpu->halt_cond);
> - }
> - qemu_wait_io_event_common(cpu);
> } while (!cpu->unplug || cpu_can_run(cpu));
>
> whpx_destroy_vcpu(cpu);