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Re: [Qemu-devel] [RFC v4 04/71] cpu: make qemu_work_cond per-cpu
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [RFC v4 04/71] cpu: make qemu_work_cond per-cpu |
Date: |
Tue, 30 Oct 2018 12:27:51 +0000 |
User-agent: |
mu4e 1.1.0; emacs 26.1.50 |
Emilio G. Cota <address@hidden> writes:
> This eliminates the need to use the BQL to queue CPU work.
>
> While at it, give the per-cpu field a generic name ("cond") since
> it will soon be used for more than just queueing CPU work.
>
> Signed-off-by: Emilio G. Cota <address@hidden>
Reviewed-by: Alex Bennée <address@hidden>
> ---
> include/qom/cpu.h | 6 ++--
> cpus-common.c | 72 ++++++++++++++++++++++++++++++++++++++---------
> cpus.c | 2 +-
> qom/cpu.c | 1 +
> 4 files changed, 63 insertions(+), 18 deletions(-)
>
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 7fdb5a2be0..2fad537a4f 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -316,6 +316,7 @@ struct qemu_work_item;
> * @mem_io_vaddr: Target virtual address at which the memory was accessed.
> * @kvm_fd: vCPU file descriptor for KVM.
> * @lock: Lock to prevent multiple access to per-CPU fields.
> + * @cond: Condition variable for per-CPU events.
> * @work_list: List of pending asynchronous work.
> * @trace_dstate_delayed: Delayed changes to trace_dstate (includes all
> changes
> * to @trace_dstate).
> @@ -358,6 +359,7 @@ struct CPUState {
>
> QemuMutex lock;
> /* fields below protected by @lock */
> + QemuCond cond;
> QSIMPLEQ_HEAD(, qemu_work_item) work_list;
>
> CPUAddressSpace *cpu_ases;
> @@ -769,12 +771,10 @@ bool cpu_is_stopped(CPUState *cpu);
> * @cpu: The vCPU to run on.
> * @func: The function to be executed.
> * @data: Data to pass to the function.
> - * @mutex: Mutex to release while waiting for @func to run.
> *
> * Used internally in the implementation of run_on_cpu.
> */
> -void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data,
> - QemuMutex *mutex);
> +void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data
> data);
>
> /**
> * run_on_cpu:
> diff --git a/cpus-common.c b/cpus-common.c
> index 2913294cb7..71469c85ce 100644
> --- a/cpus-common.c
> +++ b/cpus-common.c
> @@ -26,7 +26,6 @@
> static QemuMutex qemu_cpu_list_lock;
> static QemuCond exclusive_cond;
> static QemuCond exclusive_resume;
> -static QemuCond qemu_work_cond;
>
> /* >= 1 if a thread is inside start_exclusive/end_exclusive. Written
> * under qemu_cpu_list_lock, read with atomic operations.
> @@ -42,7 +41,6 @@ void qemu_init_cpu_list(void)
> qemu_mutex_init(&qemu_cpu_list_lock);
> qemu_cond_init(&exclusive_cond);
> qemu_cond_init(&exclusive_resume);
> - qemu_cond_init(&qemu_work_cond);
> }
>
> void cpu_list_lock(void)
> @@ -113,23 +111,37 @@ struct qemu_work_item {
> bool free, exclusive, done;
> };
>
> -static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
> +/* Called with the CPU's lock held */
> +static void queue_work_on_cpu_locked(CPUState *cpu, struct qemu_work_item
> *wi)
> {
> - qemu_mutex_lock(&cpu->lock);
> QSIMPLEQ_INSERT_TAIL(&cpu->work_list, wi, node);
> wi->done = false;
> - qemu_mutex_unlock(&cpu->lock);
>
> qemu_cpu_kick(cpu);
> }
>
> -void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data,
> - QemuMutex *mutex)
> +static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
> +{
> + cpu_mutex_lock(cpu);
> + queue_work_on_cpu_locked(cpu, wi);
> + cpu_mutex_unlock(cpu);
> +}
> +
> +void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
> {
> struct qemu_work_item wi;
> + bool has_bql = qemu_mutex_iothread_locked();
> +
> + g_assert(no_cpu_mutex_locked());
>
> if (qemu_cpu_is_self(cpu)) {
> - func(cpu, data);
> + if (has_bql) {
> + func(cpu, data);
> + } else {
> + qemu_mutex_lock_iothread();
> + func(cpu, data);
> + qemu_mutex_unlock_iothread();
> + }
> return;
> }
>
> @@ -139,13 +151,34 @@ void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func,
> run_on_cpu_data data,
> wi.free = false;
> wi.exclusive = false;
>
> - queue_work_on_cpu(cpu, &wi);
> + cpu_mutex_lock(cpu);
> + queue_work_on_cpu_locked(cpu, &wi);
> +
> + /*
> + * We are going to sleep on the CPU lock, so release the BQL.
> + *
> + * During the transition to per-CPU locks, we release the BQL _after_
> + * having kicked the destination CPU (from queue_work_on_cpu_locked
> above).
> + * This makes sure that the enqueued work will be seen by the CPU
> + * after being woken up from the kick, since the CPU sleeps on the BQL.
> + * Once we complete the transition to per-CPU locks, we will release
> + * the BQL earlier in this function.
> + */
> + if (has_bql) {
> + qemu_mutex_unlock_iothread();
> + }
> +
> while (!atomic_mb_read(&wi.done)) {
> CPUState *self_cpu = current_cpu;
>
> - qemu_cond_wait(&qemu_work_cond, mutex);
> + qemu_cond_wait(&cpu->cond, &cpu->lock);
> current_cpu = self_cpu;
> }
> + cpu_mutex_unlock(cpu);
> +
> + if (has_bql) {
> + qemu_mutex_lock_iothread();
> + }
> }
>
> void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data
> data)
> @@ -307,6 +340,7 @@ void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func
> func,
> void process_queued_cpu_work(CPUState *cpu)
> {
> struct qemu_work_item *wi;
> + bool has_bql = qemu_mutex_iothread_locked();
>
> qemu_mutex_lock(&cpu->lock);
> if (QSIMPLEQ_EMPTY(&cpu->work_list)) {
> @@ -324,13 +358,23 @@ void process_queued_cpu_work(CPUState *cpu)
> * BQL, so it goes to sleep; start_exclusive() is sleeping too,
> so
> * neither CPU can proceed.
> */
> - qemu_mutex_unlock_iothread();
> + if (has_bql) {
> + qemu_mutex_unlock_iothread();
> + }
> start_exclusive();
> wi->func(cpu, wi->data);
> end_exclusive();
> - qemu_mutex_lock_iothread();
> + if (has_bql) {
> + qemu_mutex_lock_iothread();
> + }
> } else {
> - wi->func(cpu, wi->data);
> + if (has_bql) {
> + wi->func(cpu, wi->data);
> + } else {
> + qemu_mutex_lock_iothread();
> + wi->func(cpu, wi->data);
> + qemu_mutex_unlock_iothread();
> + }
> }
> qemu_mutex_lock(&cpu->lock);
> if (wi->free) {
> @@ -340,5 +384,5 @@ void process_queued_cpu_work(CPUState *cpu)
> }
> }
> qemu_mutex_unlock(&cpu->lock);
> - qemu_cond_broadcast(&qemu_work_cond);
> + qemu_cond_broadcast(&cpu->cond);
> }
> diff --git a/cpus.c b/cpus.c
> index 38cc9e1278..d0b7f8e02d 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -1236,7 +1236,7 @@ void qemu_init_cpu_loop(void)
>
> void run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
> {
> - do_run_on_cpu(cpu, func, data, &qemu_global_mutex);
> + do_run_on_cpu(cpu, func, data);
> }
>
> static void qemu_kvm_destroy_vcpu(CPUState *cpu)
> diff --git a/qom/cpu.c b/qom/cpu.c
> index d0758c907d..bb031a3a6a 100644
> --- a/qom/cpu.c
> +++ b/qom/cpu.c
> @@ -373,6 +373,7 @@ static void cpu_common_initfn(Object *obj)
> cpu->nr_threads = 1;
>
> qemu_mutex_init(&cpu->lock);
> + qemu_cond_init(&cpu->cond);
> QSIMPLEQ_INIT(&cpu->work_list);
> QTAILQ_INIT(&cpu->breakpoints);
> QTAILQ_INIT(&cpu->watchpoints);
--
Alex Bennée
- [Qemu-devel] [RFC v4 38/71] i386/kvm: convert to cpu_interrupt_request, (continued)
- [Qemu-devel] [RFC v4 38/71] i386/kvm: convert to cpu_interrupt_request, Emilio G. Cota, 2018/10/25
- [Qemu-devel] [RFC v4 22/71] mips: convert to cpu_halted, Emilio G. Cota, 2018/10/25
- [Qemu-devel] [RFC v4 23/71] riscv: convert to cpu_halted, Emilio G. Cota, 2018/10/25
- [Qemu-devel] [RFC v4 20/71] lm32: convert to cpu_halted, Emilio G. Cota, 2018/10/25
- [Qemu-devel] [RFC v4 11/71] m68k: convert to helper_cpu_halted_set, Emilio G. Cota, 2018/10/25
- [Qemu-devel] [RFC v4 04/71] cpu: make qemu_work_cond per-cpu, Emilio G. Cota, 2018/10/25
- [Qemu-devel] [RFC v4 00/71] per-CPU locks, Emilio G. Cota, 2018/10/25
- Re: [Qemu-devel] [RFC v4 01/71] cpu: convert queued work to a QSIMPLEQ, Alex Bennée, 2018/10/29