Block Thread Affinity

Introduction

In the thread-per-block scheduler, you can set the block's core affinity. Each block can be pinned to a group cores or be set back to use the standard kernel scheduler.

The implementation is done by adding new functions to the GRUEL library:

  gr_thread_t get_current_thread_id();
  void thread_bind_to_processor(unsigned int n);
  void thread_bind_to_processor(const std::vector<unsigned int> &mask);
  void thread_bind_to_processor(gr_thread_t thread, unsigned int n);
  void thread_bind_to_processor(gr_thread_t thread, const std::vector<unsigned int> &mask);
  void thread_unbind();
  void thread_unbind(gr_thread_t thread);

The ability to set a thread's affinity to a core or groups of cores is not implemented in the Boost thread library, and so we have made our own portability library. In particular, the gruel::gr_thread_t type is defined as the thread type for the given system. The other functions are designed to be portable as well by calling the specific implementation for the thread affinity for a particular platform.

There are functions to set a thread to a group of cores. If the thread is not given, the current thread is used. If a single number is passed, only that core is set (this is equivalent to a core mask with just a single value).

Similarly, there are functions to unset the affinity. This practically implements the setting of the thread's affinity to all possible cores. Again, the function that does not take a thread argument unsets the affinity for the current thread.

GNU Radio Block API

Each block has two new data members:

• threaded: a boolean value that is true if the block is attached to a thread.
• thread: a gruel::gr_thread_t handle to the block's thread.

A block can set and unset it's affinity at any time using the following member functions:

• gr_block::set_processor_affinity(const std::vector<unsigned int> &mask)
• gr_block::unset_processor_affinity()

Where mask is a vector of core numbers to set the thread's affinity to.

The current core affinity can be retrieved using the member function:

• gr_block::processor_affinity()

When set before the flowgraph is started, the scheduler will set the thread's affinity when it is started. When already running, the block's affinity will be immediately set.