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[PATCH v10 03/73] cpu: make qemu_work_cond per-cpu
From: |
Robert Foley |
Subject: |
[PATCH v10 03/73] cpu: make qemu_work_cond per-cpu |
Date: |
Wed, 17 Jun 2020 17:01:21 -0400 |
From: "Emilio G. Cota" <cota@braap.org>
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.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Robert Foley <robert.foley@linaro.org>
---
cpus-common.c | 72 ++++++++++++++++++++++++++++++++++---------
cpus.c | 2 +-
hw/core/cpu.c | 1 +
include/hw/core/cpu.h | 6 ++--
4 files changed, 63 insertions(+), 18 deletions(-)
diff --git a/cpus-common.c b/cpus-common.c
index 622430bd33..57d9fc6ea1 100644
--- a/cpus-common.c
+++ b/cpus-common.c
@@ -27,7 +27,6 @@
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.
@@ -43,7 +42,6 @@ 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)
@@ -103,23 +101,37 @@ 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;
}
@@ -129,13 +141,34 @@ 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)
@@ -299,6 +332,7 @@ 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)) {
@@ -316,13 +350,23 @@ 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) {
@@ -332,5 +376,5 @@ 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 ca271411a4..035f41a997 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1216,7 +1216,7 @@ 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/hw/core/cpu.c b/hw/core/cpu.c
index 1cba5b6e69..07251d83df 100644
--- a/hw/core/cpu.c
+++ b/hw/core/cpu.c
@@ -370,6 +370,7 @@ 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);
diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 4d4006f1fb..ebff239ad3 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -333,6 +333,7 @@ struct qemu_work_item;
* @kvm_fd: vCPU file descriptor for KVM.
* @lock: Lock to prevent multiple access to per-CPU fields. Must be acquired
* after the BQL.
+ * @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).
@@ -378,6 +379,7 @@ struct CPUState {
QemuMutex lock;
/* fields below protected by @lock */
+ QemuCond cond;
QSIMPLEQ_HEAD(, qemu_work_item) work_list;
CPUAddressSpace *cpu_ases;
@@ -774,12 +776,10 @@ 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:
--
2.17.1
- [PATCH v10 00/73] per-CPU locks, Robert Foley, 2020/06/17
- [PATCH v10 01/73] cpu: rename cpu->work_mutex to cpu->lock, Robert Foley, 2020/06/17
- [PATCH v10 03/73] cpu: make qemu_work_cond per-cpu,
Robert Foley <=
- [PATCH v10 02/73] cpu: introduce cpu_mutex_lock/unlock, Robert Foley, 2020/06/17
- [PATCH v10 04/73] cpu: move run_on_cpu to cpus-common, Robert Foley, 2020/06/17
- [PATCH v10 06/73] cpu: make per-CPU locks an alias of the BQL in TCG rr mode, Robert Foley, 2020/06/17
- [PATCH v10 05/73] cpu: introduce process_queued_cpu_work_locked, Robert Foley, 2020/06/17
- [PATCH v10 10/73] hppa: convert to helper_cpu_halted_set, Robert Foley, 2020/06/17
- [PATCH v10 11/73] m68k: convert to helper_cpu_halted_set, Robert Foley, 2020/06/17
- [PATCH v10 07/73] tcg-runtime: define helper_cpu_halted_set, Robert Foley, 2020/06/17
- [PATCH v10 09/73] cris: convert to helper_cpu_halted_set, Robert Foley, 2020/06/17
- [PATCH v10 08/73] ppc: convert to helper_cpu_halted_set, Robert Foley, 2020/06/17
- [PATCH v10 14/73] cpu: define cpu_halted helpers, Robert Foley, 2020/06/17