[PATCH v2 1/1] libcamera: add method to set thread affinity

[Harvey Yang]

From: Han-Lin Chen <hanlinchen at chromium.org>

Add method to set thread affinity to Thread class.

Signed-off-by: Han-Lin Chen <hanlinchen at chromium.org>
Co-developed-by: Harvey Yang <chenghaoyang at chromium.org>
Signed-off-by: Harvey Yang <chenghaoyang at chromium.org>
---
 include/libcamera/base/thread.h |  6 +++++
 src/libcamera/base/thread.cpp   | 47 +++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/include/libcamera/base/thread.h b/include/libcamera/base/thread.h
index 4f33de63d..c74fe102b 100644
--- a/include/libcamera/base/thread.h
+++ b/include/libcamera/base/thread.h
@@ -35,6 +35,8 @@ public:
 	void exit(int code = 0);
 	bool wait(utils::duration duration = utils::duration::max());
 
+	void setThreadAffinity(const std::vector<int> &cpus);
+
 	bool isRunning();
 
 	Signal<> finished;
@@ -54,6 +56,8 @@ private:
 	void startThread();
 	void finishThread();
 
+	void setThreadAffinityInternal();
+
 	void postMessage(std::unique_ptr<Message> msg, Object *receiver);
 	void removeMessages(Object *receiver);
 
@@ -67,6 +71,8 @@ private:
 
 	std::thread thread_;
 	ThreadData *data_;
+
+	std::vector<int> cpus_;
 };
 
 } /* namespace libcamera */
diff --git a/src/libcamera/base/thread.cpp b/src/libcamera/base/thread.cpp
index 8735670b8..de5423eda 100644
--- a/src/libcamera/base/thread.cpp
+++ b/src/libcamera/base/thread.cpp
@@ -254,6 +254,8 @@ void Thread::start()
 	data_->exit_.store(false, std::memory_order_relaxed);
 
 	thread_ = std::thread(&Thread::startThread, this);
+
+	setThreadAffinityInternal();
 }
 
 void Thread::startThread()
@@ -410,6 +412,51 @@ bool Thread::wait(utils::duration duration)
 	return hasFinished;
 }
 
+/**
+ * \brief Set the CPU affinity mask of the thread
+ * \param[in] cpus The list of CPU indices that the thread is set affinity to
+ */
+void Thread::setThreadAffinity(const std::vector<int> &cpus)
+{
+	cpus_.clear();
+
+	const unsigned int num_cpus = std::thread::hardware_concurrency();
+	for (const int &cpu : cpus) {
+		if (cpus_.size() == CPU_SETSIZE) {
+			LOG(Thread, Error) << "cpus_ already contains " << CPU_SETSIZE
+					   << " cpus. Ignoring the rest.";
+			break;
+		}
+
+		if (cpu >= static_cast<int>(num_cpus) || cpu < 0) {
+			LOG(Thread, Error) << "Ignore an invalid cpu index: " << cpu;
+			continue;
+		}
+
+		cpus_.push_back(cpu);
+	}
+
+	MutexLocker locker(data_->mutex_);
+	if (data_->running_)
+		setThreadAffinityInternal();
+}
+
+void Thread::setThreadAffinityInternal()
+{
+	if (cpus_.empty())
+		return;
+
+	auto handle = thread_.native_handle();
+
+	cpu_set_t cpuset;
+	CPU_ZERO(&cpuset);
+
+	for (auto cpu : cpus_)
+		CPU_SET(cpu, &cpuset);
+
+	pthread_setaffinity_np(handle, sizeof(cpu_set_t), &cpuset);
+}
+
 /**
  * \brief Check if the thread is running
  *
-- 
2.47.0.rc1.288.g06298d1525-goog