From 4d9db06d669044c0c461a2aed79c85c7fe32a502 Mon Sep 17 00:00:00 2001
From: Han-Lin Chen <hanlinchen@chromium.org>
Date: Tue, 29 Oct 2024 08:57:55 +0000
Subject: libcamera: add method to set thread affinity

Add method to set thread affinity to Thread class.

Signed-off-by: Han-Lin Chen <hanlinchen@chromium.org>
Co-developed-by: Harvey Yang <chenghaoyang@chromium.org>
Signed-off-by: Harvey Yang <chenghaoyang@chromium.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
---
 src/libcamera/base/thread.cpp | 47 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

(limited to 'src')

diff --git a/src/libcamera/base/thread.cpp b/src/libcamera/base/thread.cpp
index 8735670b..f6322fe3 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_;
 };
 
 /**
@@ -281,6 +284,8 @@ void Thread::startThread()
 	data_->tid_ = syscall(SYS_gettid);
 	currentThreadData = data_;
 
+	setThreadAffinityInternal();
+
 	run();
 }
 
@@ -410,6 +415,48 @@ 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()).
+ * If any index is invalid, this function won't modify the thread affinity and
+ * will return an error.
+ *
+ * \return 0 if all indices are valid, -EINVAL otherwise
+ */
+int 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());
+
+	for (const unsigned int &cpu : cpus) {
+		if (cpu >= numCpus) {
+			LOG(Thread, Error) << "Invalid CPU " << cpu << "for thread affinity";
+			return -EINVAL;
+		}
+
+		CPU_SET(cpu, &data_->cpuset_.value());
+	}
+
+	if (data_->running_)
+		setThreadAffinityInternal();
+
+	return 0;
+}
+
+void Thread::setThreadAffinityInternal()
+{
+	if (!data_->cpuset_)
+		return;
+
+	const cpu_set_t &cpuset = data_->cpuset_.value();
+	pthread_setaffinity_np(thread_.native_handle(), sizeof(cpuset), &cpuset);
+}
+
 /**
  * \brief Check if the thread is running
  *
-- 
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