commit f07df42d49c0a66d6d9ded7c975faef50fca7eca
author Andrew Boie <andrew.p.boie@intel.com> Fri Nov 06 13:11:12 2020 -0800
committer Christopher Friedt <chrisfriedt@gmail.com> Fri Jul 30 20:16:47 2021 -0400
tree d1411afae540bb47744aea089d292881283f69e7
parent c661765f1d4d479a24b240f9fae2752eb1fc0aa6

kernel: make k_current_get() work without syscall

We cache the current thread ID in a thread-local variable
at thread entry, and have k_current_get() return that,
eliminating system call overhead for this API.

DL: changed _current to use z_current_get() as it is
    being used during boot where TLS is not available.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
Signed-off-by: Daniel Leung <daniel.leung@intel.com>

include/kernel.h

diff --git a/include/kernel.h b/include/kernel.h
index 49a6727..4c2aea5 100644
--- a/include/kernel.h
+++ b/include/kernel.h
@@ -490,10 +490,32 @@
 /**
  * @brief Get thread ID of the current thread.
  *
+ * This unconditionally queries the kernel via a system call.
+ *
+ * @return ID of current thread.
+ */
+__syscall k_tid_t z_current_get(void);
+
+#ifdef CONFIG_THREAD_LOCAL_STORAGE
+/* Thread-local cache of current thread ID, set in z_thread_entry() */
+extern __thread k_tid_t z_tls_current;
+#endif
+
+/**
+ * @brief Get thread ID of the current thread.
+ *
  * @return ID of current thread.
  *
  */
-__syscall k_tid_t k_current_get(void) __attribute_const__;
+__attribute_const__
+static inline k_tid_t k_current_get(void)
+{
+#ifdef CONFIG_THREAD_LOCAL_STORAGE
+	return z_tls_current;
+#else
+	return z_current_get();
+#endif
+}
 
 /**
  * @brief Abort a thread.

include/kernel_structs.h

diff --git a/include/kernel_structs.h b/include/kernel_structs.h
index 50945aa..e4c79a5 100644
--- a/include/kernel_structs.h
+++ b/include/kernel_structs.h
@@ -187,7 +187,7 @@
 
 #define _current_cpu ({ __ASSERT_NO_MSG(!z_smp_cpu_mobile()); \
 			arch_curr_cpu(); })
-#define _current k_current_get()
+#define _current z_current_get()
 
 #else
 #define _current_cpu (&_kernel.cpus[0])

kernel/sched.c

diff --git a/kernel/sched.c b/kernel/sched.c
index c5e5670..c49354c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1365,7 +1365,7 @@
 #include <syscalls/k_wakeup_mrsh.c>
 #endif
 
-k_tid_t z_impl_k_current_get(void)
+k_tid_t z_impl_z_current_get(void)
 {
 #ifdef CONFIG_SMP
 	/* In SMP, _current is a field read from _current_cpu, which
@@ -1384,11 +1384,11 @@
 }
 
 #ifdef CONFIG_USERSPACE
-static inline k_tid_t z_vrfy_k_current_get(void)
+static inline k_tid_t z_vrfy_z_current_get(void)
 {
-	return z_impl_k_current_get();
+	return z_impl_z_current_get();
 }
-#include <syscalls/k_current_get_mrsh.c>
+#include <syscalls/z_current_get_mrsh.c>
 #endif
 
 int z_impl_k_is_preempt_thread(void)

lib/os/thread_entry.c

diff --git a/lib/os/thread_entry.c b/lib/os/thread_entry.c
index aa3722d..4a8be64 100644
--- a/lib/os/thread_entry.c
+++ b/lib/os/thread_entry.c
@@ -13,6 +13,10 @@
 
 #include <kernel.h>
 
+#ifdef CONFIG_THREAD_LOCAL_STORAGE
+__thread k_tid_t z_tls_current;
+#endif
+
 /*
  * Common thread entry point function (used by all threads)
  *
@@ -26,6 +30,9 @@
 FUNC_NORETURN void z_thread_entry(k_thread_entry_t entry,
 				 void *p1, void *p2, void *p3)
 {
+#ifdef CONFIG_THREAD_LOCAL_STORAGE
+	z_tls_current = z_current_get();
+#endif
 	entry(p1, p2, p3);
 
 	k_thread_abort(k_current_get());