[PATCH v3 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 |  5 ++++
 src/libcamera/base/thread.cpp   | 52 +++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/include/libcamera/base/thread.h b/include/libcamera/base/thread.h
index 4f33de63d..58cae341b 100644
--- a/include/libcamera/base/thread.h
+++ b/include/libcamera/base/thread.h
@@ -15,6 +15,7 @@
 
 #include <libcamera/base/message.h>
 #include <libcamera/base/signal.h>
+#include <libcamera/base/span.h>
 #include <libcamera/base/utils.h>
 
 namespace libcamera {
@@ -35,6 +36,8 @@ public:
 	void exit(int code = 0);
 	bool wait(utils::duration duration = utils::duration::max());
 
+	void setThreadAffinity(const Span<const unsigned int> &cpus);
+
 	bool isRunning();
 
 	Signal<> finished;
@@ -54,6 +57,8 @@ private:
 	void startThread();
 	void finishThread();
 
+	void setThreadAffinityInternal();
+
 	void postMessage(std::unique_ptr<Message> msg, Object *receiver);
 	void removeMessages(Object *receiver);
 
diff --git a/src/libcamera/base/thread.cpp b/src/libcamera/base/thread.cpp
index 8735670b8..f40c7d8e7 100644
--- a/src/libcamera/base/thread.cpp
+++ b/src/libcamera/base/thread.cpp
@@ -9,6 +9,7 @@
 
 #include <atomic>
 #include <list>
+#include <optional>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -128,6 +129,8 @@ private:
 	int exitCode_;
 
 	MessageQueue messages_;
+
+	std::optional<cpu_set_t> cpuset_ = std::nullopt;
 };
 
 /**
@@ -254,6 +257,8 @@ void Thread::start()
 	data_->exit_.store(false, std::memory_order_relaxed);
 
 	thread_ = std::thread(&Thread::startThread, this);
+
+	setThreadAffinityInternal();
 }
 
 void Thread::startThread()
@@ -410,6 +415,53 @@ 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
+ *
+ * The cpu indices should be within [0, std::thread::hardware_concurrency()),
+ * and the total number should not exceed `CPU_SETSIZE`. Invalid indices and
+ * extra indices will be ignored.
+ */
+void Thread::setThreadAffinity(const Span<const unsigned int> &cpus)
+{
+	const unsigned int numCpus = std::thread::hardware_concurrency();
+
+	MutexLocker locker(data_->mutex_);
+	data_->cpuset_ = cpu_set_t();
+	CPU_ZERO(&data_->cpuset_.value());
+
+	unsigned int count = 0;
+	for (const unsigned int &cpu : cpus) {
+		if (count == CPU_SETSIZE) {
+			LOG(Thread, Error) << "cpus_ already contains " << CPU_SETSIZE
+					   << " cpus. Ignoring the rest.";
+			break;
+		}
+
+		if (cpu >= numCpus) {
+			LOG(Thread, Error) << "Ignore an invalid cpu index: " << cpu;
+			continue;
+		}
+
+		++count;
+		CPU_SET(cpu, &data_->cpuset_.value());
+	}
+
+	if (data_->running_)
+		setThreadAffinityInternal();
+}
+
+void Thread::setThreadAffinityInternal()
+{
+	if (!data_->cpuset_)
+		return;
+
+	auto handle = thread_.native_handle();
+
+	pthread_setaffinity_np(handle, sizeof(cpu_set_t), &data_->cpuset_.value());
+}
+
 /**
  * \brief Check if the thread is running
  *
-- 
2.47.0.rc1.288.g06298d1525-goog