kern: proc: Add enhanced processor arbitration

Unlike the previouses systems where there was a global arbiter and a
shared lock, rv7 derives a zero-based processor index by using the lower
8 bits of the pid MOD the core count. This significantly reduces
contention.

Signed-off-by: Ian Moffett <ian@osmora.org>

4 files changed, 112 insertions, 0 deletions

diff --git a/sys/inc/os/process.h b/sys/inc/os/process.h
index a2e3fdd..24db3e1 100644
--- a/sys/inc/os/process.h
+++ b/sys/inc/os/process.h
@@ -43,11 +43,13 @@
  * system
  *
  * @pid: Process ID
+ * @affinity: Processor affinity
  * @pcb: Process control block
  * @link: Queue link
  */
 struct process {
     pid_t pid;
+    id_t affinity;
     struct pcb pcb;
     TAILQ_ENTRY(process) link;
 };
diff --git a/sys/inc/os/sched.h b/sys/inc/os/sched.h
new file mode 100644
index 0000000..c0355c6
--- /dev/null
+++ b/sys/inc/os/sched.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _OS_SCHED_H_
+#define _OS_SCHED_H_
+
+#include <sys/types.h>
+#include <os/process.h>
+#include <mu/cpu.h>
+
+/*
+ * Enqueue a process into a runqueue and return the processor
+ * now associated
+ */
+struct cpu_info *sched_enqueue_proc(struct process *proc);
+
+#endif  /* !_OS_SCHED_H_ */
diff --git a/sys/os/os_process.c b/sys/os/os_process.c
index 6bfa220..c80dcc4 100644
--- a/sys/os/os_process.c
+++ b/sys/os/os_process.c
@@ -43,6 +43,7 @@ process_init(struct process *process, uintptr_t ip, int flags)
     }
 
     process->pid = next_pid;
+    process->affinity = -1;
     atomic_inc_64(&next_pid);
     mu_process_init(process, ip, flags);
     return 0;
diff --git a/sys/os/os_sched.c b/sys/os/os_sched.c
new file mode 100644
index 0000000..e0dfc98
--- /dev/null
+++ b/sys/os/os_sched.c
@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/queue.h>
+#include <os/sched.h>
+#include <os/trace.h>
+#include <mu/cpu.h>
+
+struct cpu_info *
+sched_enqueue_proc(struct process *proc)
+{
+    struct cpu_info *core;
+    size_t ncpu, i;
+
+    if (proc == NULL) {
+        return NULL;
+    }
+
+    if (proc->affinity >= 0) {
+        if ((core = cpu_get(proc->affinity)) != NULL)
+            return core;
+    }
+
+    /*
+     * Here, we derive the processor index by using the lower
+     * byte MOD the number of cores, this works best and most
+     * evenly when the PID assignment increments monotonically
+     * though could potentially work with random assignment, just
+     * more sporadic.
+     */
+    ncpu = cpu_count();
+    i = (proc->pid & 0xFF) % ncpu;
+    while ((core = cpu_get(i++)) == NULL) {
+        if (i > ncpu) {
+            i = 0;
+        }
+    }
+    TAILQ_INSERT_TAIL(&core->pqueue, proc, link);
+    return core;
+}