[PATCH v7 1/1] libcamera: add method to set thread affinity

[Kieran Bingham]

Quoting Harvey Yang (2024-10-29 08:57:55)
> 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>

Looks good to me.


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> ---
>  include/libcamera/base/thread.h |  5 ++++
>  src/libcamera/base/thread.cpp   | 47 +++++++++++++++++++++++++++++++++
>  test/threads.cpp                | 40 ++++++++++++++++++++++++++++
>  3 files changed, 92 insertions(+)
> 
> diff --git a/include/libcamera/base/thread.h b/include/libcamera/base/thread.h
> index 4f33de63d..3209d4f7c 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());
>  
> +       int 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..f6322fe31 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
>   *
> diff --git a/test/threads.cpp b/test/threads.cpp
> index ceb4fa0f2..8d6ee1510 100644
> --- a/test/threads.cpp
> +++ b/test/threads.cpp
> @@ -9,9 +9,11 @@
>  #include <iostream>
>  #include <memory>
>  #include <pthread.h>
> +#include <sched.h>
>  #include <thread>
>  #include <time.h>
>  
> +#include <libcamera/base/object.h>
>  #include <libcamera/base/thread.h>
>  
>  #include "test.h"
> @@ -66,6 +68,27 @@ private:
>         bool &cancelled_;
>  };
>  
> +class CpuSetTester : public Object
> +{
> +public:
> +       CpuSetTester(unsigned int cpuset)
> +               : cpuset_(cpuset) {}
> +
> +       bool testCpuSet()
> +       {
> +               int ret = sched_getcpu();
> +               if (static_cast<int>(cpuset_) != ret) {
> +                       cout << "Invalid cpuset: " << ret << ", expecting: " << cpuset_ << endl;
> +                       return false;
> +               }
> +
> +               return true;
> +       }
> +
> +private:
> +       const unsigned int cpuset_;
> +};
> +
>  class ThreadTest : public Test
>  {
>  protected:
> @@ -165,6 +188,23 @@ protected:
>                         return TestFail;
>                 }
>  
> +               const unsigned int numCpus = std::thread::hardware_concurrency();
> +               for (unsigned int i = 0; i < numCpus; ++i) {
> +                       thread = std::make_unique<Thread>();
> +                       const std::array<const unsigned int, 1> cpus{ i };
> +                       thread->setThreadAffinity(cpus);
> +                       thread->start();
> +
> +                       CpuSetTester tester(i);
> +                       tester.moveToThread(thread.get());
> +
> +                       if (!tester.invokeMethod(&CpuSetTester::testCpuSet, ConnectionTypeBlocking))
> +                               return TestFail;
> +
> +                       thread->exit(0);
> +                       thread->wait();
> +               }
> +
>                 return TestPass;
>         }
>  
> -- 
> 2.47.0.163.g1226f6d8fa-goog
>