feat: Implement peek in ps

runtime/include/arch/x86_64/context.h

@@ -5,6 +5,7 @@
 #include <string.h>
 #include <ucontext.h>
 #include <unistd.h>
+#include <stdbool.h>
 
 #define ARCH_NREGS       (16 /* GP registers */ + 1 /* for IP */)
 #define ARCH_SIG_JMP_OFF 8
@@ -74,27 +75,38 @@ static void __attribute__((noinline)) arch_context_init(arch_context_t *actx, re
 	*(actx->regs + 16) = ip;
 }
 
+/**
+ * Preempt the current sandbox and start executing the next sandbox
+ * @param mc - the context of the current thread of execution
+ * @param ctx - the context that we want to restore
+ * @return {0,1} 0 = context restored successfully. 1 = special processing because thread was last in a user-level
+ * context switch state
+ **/
 static int
 arch_mcontext_restore(mcontext_t *mc, arch_context_t *ctx)
 {
 	assert(ctx != &worker_thread_base_context);
 
-	// if ctx->regs[5] is set, this was last in a user-level context switch state!
-	// else restore mcontext..
-	if (ctx->regs[5]) {
+	// if ctx->regs[5] is set, this was last in a user-level context switch state
+	bool did_user_level_context_switch = ctx->regs[5];
+	if (did_user_level_context_switch) {
 		mc->gregs[REG_RSP] = ctx->regs[5];
 		mc->gregs[REG_RIP] = ctx->regs[16] + ARCH_SIG_JMP_OFF;
 		ctx->regs[5]       = 0;
-
 		return 1;
 	} else {
+		// Restore mcontext
 		memcpy(mc, &ctx->mctx, sizeof(mcontext_t));
 		memset(&ctx->mctx, 0, sizeof(mcontext_t));
-	}
-
 		return 0;
 	}
+}
 
+/**
+ * Save the context of the currently executing process
+ * @param ctx - destination
+ * @param mc - source
+ **/
 static void
 arch_mcontext_save(arch_context_t *ctx, mcontext_t *mc)
 {
@@ -104,27 +116,26 @@ arch_mcontext_save(arch_context_t *ctx, mcontext_t *mc)
 	memcpy(&ctx->mctx, mc, sizeof(mcontext_t));
 }
 
-
+/**
+ * @param current - the registers and context of the thing running
+ * @param next - the registers and context of what we're switching to
+ * @return always returns 0, indicating success
+ *
+ * NULL in either of these values indicates the "no sandbox to execute" state,
+ * which defaults to resuming execution of main
+ **/
 static inline int
-arch_context_switch(arch_context_t *ca, arch_context_t *na)
+arch_context_switch(arch_context_t *current, arch_context_t *next)
 {
-	if (!ca) {
-		assert(na);
-		// switching from "no sandbox to execute" state to "executing a sandbox"
-		ca = &worker_thread_base_context;
-	} else if (!na) {
-		assert(ca);
-
-		// switching from "executing a sandbox" to "no execution" state.
-		na = &worker_thread_base_context;
-	} else {
-		assert(na && ca);
+	// if both current and next are NULL, there is no state change
+	assert(current != NULL || next != NULL);
 
-		// switching between sandboxes.
-	}
+	// Set any NULLs to worker_thread_base_context to resume execution of main
+	if (current == NULL) current = &worker_thread_base_context;
+	if (next == NULL) next = &worker_thread_base_context;
 
-	reg_t *cr = ca->regs, *nr = na->regs;
-	assert(cr && nr);
+	reg_t *current_registers = current->regs, *next_registers = next->regs;
+	assert(current_registers && next_registers);
 
 	asm volatile("pushq %%rbp\n\t"
 	             "movq %%rsp, %%rbp\n\t"
@@ -143,7 +154,7 @@ arch_context_switch(arch_context_t *ca, arch_context_t *na)
 	             "3:\n\t"
 	             "popq %%rbp\n\t"
 	             :
-	             : "a"(cr), "b"(nr)
+	             : "a"(current_registers), "b"(next_registers)
 	             : "memory", "cc", "rcx", "rdx", "rsi", "rdi", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15",
 	               "xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7", "xmm8", "xmm9", "xmm10", "xmm11",
 	               "xmm12", "xmm13", "xmm14", "xmm15");

runtime/include/sandbox.h

@@ -88,7 +88,6 @@ extern __thread arch_context_t *worker_thread_next_context;
 
 extern void worker_thread_block_current_sandbox(void);
 extern void worker_thread_exit_current_sandbox(void);
-extern struct sandbox *worker_thread_get_next_sandbox(void);
 extern void worker_thread_process_io(void);
 extern void __attribute__((noreturn)) worker_thread_sandbox_switch_preempt(void);
 extern void worker_thread_wakeup_sandbox(sandbox_t *sandbox);

runtime/include/sandbox_run_queue.h

@@ -9,12 +9,14 @@ typedef struct sandbox *(*sandbox_run_queue_add_t)(struct sandbox *);
 typedef struct sandbox *(*sandbox_run_queue_remove_t)(void);
 typedef bool (*sandbox_run_queue_is_empty_t)(void);
 typedef void (*sandbox_run_queue_delete_t)(struct sandbox *sandbox);
+typedef struct sandbox *(*sandbox_run_queue_get_next_t)();
 
 typedef struct sandbox_run_queue_config_t {
 	sandbox_run_queue_add_t      add;
 	sandbox_run_queue_is_empty_t is_empty;
 	sandbox_run_queue_remove_t   remove;
 	sandbox_run_queue_delete_t delete;
+	sandbox_run_queue_get_next_t get_next;
 } sandbox_run_queue_config_t;
 
 
@@ -24,5 +26,7 @@ struct sandbox *sandbox_run_queue_add(struct sandbox *);
 void            sandbox_run_queue_delete(struct sandbox *);
 struct sandbox *sandbox_run_queue_remove();
 bool            sandbox_run_queue_is_empty();
+struct sandbox *sandbox_run_queue_get_next();
+
 
 #endif /* SFRT_SANDBOX_RUN_QUEUE_H */

runtime/include/software_interrupt.h

@@ -10,6 +10,7 @@
  ***************************************/
 
 extern __thread volatile sig_atomic_t software_interrupt_is_disabled;
+extern uint64_t                       SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_CYCLES;
 
 /***************************************
  * Public Static Inlines

runtime/src/main.c

@@ -198,6 +198,8 @@ main(int argc, char **argv)
 	memset(runtime_worker_threads, 0, sizeof(pthread_t) * WORKER_THREAD_CORE_COUNT);
 
 	runtime_processor_speed_MHz                    = runtime_get_processor_speed_MHz();
+	SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_CYCLES = (uint64_t)SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_USEC
+	                                                 * runtime_processor_speed_MHz;
 	printf("Detected processor speed of %f MHz\n", runtime_processor_speed_MHz);
 
 	runtime_set_resource_limits_to_max();

runtime/src/runtime.c

@@ -44,8 +44,8 @@ runtime_initialize(void)
 	assert(runtime_epoll_file_descriptor >= 0);
 
 	// Allocate and Initialize the global deque
-	// sandbox_request_scheduler_fifo_initialize();
-	sandbox_request_scheduler_ps_initialize();
+	sandbox_request_scheduler_fifo_initialize();
+	// sandbox_request_scheduler_ps_initialize();
 
 	// Mask Signals
 	software_interrupt_mask_signal(SIGUSR1);

runtime/src/sandbox.c

@@ -191,7 +191,7 @@ current_sandbox_main(void)
 	// FIXME: is this right? this is the first time this sandbox is running.. so it wont
 	//        return to worker_thread_switch_to_sandbox() api..
 	//        we'd potentially do what we'd in worker_thread_switch_to_sandbox() api here for cleanup..
-	if (!software_interrupt_is_enabled()) {
+	if (software_interrupt_is_enabled() == false) {
 		arch_context_init(&current_sandbox->ctxt, 0, 0);
 		worker_thread_next_context = NULL;
 		software_interrupt_enable();

runtime/src/sandbox_request_scheduler.c

@@ -26,3 +26,10 @@ sandbox_request_scheduler_remove()
 	assert(sandbox_request_scheduler.remove != NULL);
 	return sandbox_request_scheduler.remove();
 }
+
+uint64_t
+sandbox_request_scheduler_peek()
+{
+	assert(sandbox_request_scheduler.peek != NULL);
+	return sandbox_request_scheduler.peek();
+};

runtime/src/sandbox_run_queue.c

@@ -38,3 +38,10 @@ sandbox_run_queue_is_empty()
 {
 	return sandbox_run_queue_is_empty();
 }
+
+struct sandbox *
+sandbox_run_queue_get_next()
+{
+	assert(sandbox_run_queue.get_next != NULL);
+	return sandbox_run_queue.get_next();
+};

runtime/src/sandbox_run_queue_fifo.c

@@ -1,5 +1,6 @@
 #include "sandbox_run_queue_fifo.h"
 #include "sandbox_run_queue.h"
+#include "sandbox_request_scheduler.h"
 
 __thread static struct ps_list_head sandbox_run_queue_fifo;
 
@@ -26,6 +27,35 @@ sandbox_run_queue_fifo_remove(struct sandbox *sandbox_to_remove)
 	ps_list_rem_d(sandbox_to_remove);
 }
 
+/**
+ * Execute the sandbox at the head of the thread local runqueue
+ * If the runqueue is empty, pull a fresh batch of sandbox requests, instantiate them, and then execute the new head
+ * @return the sandbox to execute or NULL if none are available
+ **/
+struct sandbox *
+sandbox_run_queue_fifo_get_next()
+{
+	if (sandbox_run_queue_is_empty()) {
+		sandbox_request_t *sandbox_request = sandbox_request_scheduler_remove();
+		if (sandbox_request == NULL) return NULL;
+		struct sandbox *sandbox = sandbox_allocate(sandbox_request);
+		assert(sandbox);
+		free(sandbox_request);
+		sandbox->state = RUNNABLE;
+		sandbox_run_queue_add(sandbox);
+		return sandbox;
+	}
+
+	// Execute Round Robin Scheduling Logic
+	struct sandbox *next_sandbox = sandbox_run_queue_remove();
+	assert(next_sandbox->state != RETURNED);
+	sandbox_run_queue_add(next_sandbox);
+
+	debuglog("[%p: %s]\n", next_sandbox, next_sandbox->module->name);
+	return next_sandbox;
+}
+
+
 // Append a sandbox to the runqueue
 struct sandbox *
 sandbox_run_queue_fifo_append(struct sandbox *sandbox_to_append)
@@ -55,7 +85,8 @@ sandbox_run_queue_fifo_initialize()
 	sandbox_run_queue_config_t config = { .add      = sandbox_run_queue_fifo_append,
 		                              .is_empty = sandbox_run_queue_fifo_is_empty,
 		                              .remove   = sandbox_run_queue_fifo_remove_and_return,
-		                              .delete   = sandbox_run_queue_fifo_remove };
+		                              .delete   = sandbox_run_queue_fifo_remove,
+		                              .get_next = sandbox_run_queue_fifo_get_next };
 
 	sandbox_run_queue_initialize(&config);
 }

runtime/src/sandbox_run_queue_ps.c

@@ -1,6 +1,7 @@
 #include "sandbox_run_queue_ps.h"
 #include "sandbox_run_queue.h"
 #include "priority_queue.h"
+#include "sandbox_request_scheduler.h"
 
 // Local State
 __thread static struct priority_queue sandbox_run_queue_ps;
@@ -46,6 +47,61 @@ sandbox_run_queue_ps_delete(struct sandbox *sandbox)
 	assert(rc != -2);
 }
 
+/**
+ * This function determines the next sandbox to run. This is either the head of the runqueue or the
+ *
+ * Execute the sandbox at the head of the thread local runqueue
+ * If the runqueue is empty, pull a fresh batch of sandbox requests, instantiate them, and then execute the new head
+ * @return the sandbox to execute or NULL if none are available
+ **/
+struct sandbox *
+sandbox_run_queue_ps_get_next()
+{
+	// At any point, we may need to run the head of the request scheduler, the head of the local runqueue, or we
+	// might want to continue executing the current sandbox. If we want to keep executing the current sandbox, we
+	// should have a fast path to be able to resume without context switches.
+
+	// If the run queue is empty, we've run the current sandbox to completion
+
+	// We assume that the current sandbox is always on the runqueue when in a runnable state, we know it's the
+	// highest priority thing on the runqueue.
+
+	// Case 1: Current runqueue is empty, so pull from global queue and add to runqueue
+	if (sandbox_run_queue_is_empty()) {
+		sandbox_request_t *sandbox_request = sandbox_request_scheduler_remove();
+		if (sandbox_request == NULL) return NULL;
+		struct sandbox *sandbox = sandbox_allocate(sandbox_request);
+		assert(sandbox);
+		free(sandbox_request);
+		sandbox->state = RUNNABLE;
+		sandbox_run_queue_add(sandbox);
+		return sandbox;
+	}
+
+	// Case 2: Current runqueue is not empty, so compare head of runqueue to head of global request queue and return
+	// highest priority
+
+	uint64_t global_deadline = sandbox_request_scheduler_peek() - SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_CYCLES;
+	// This should be refactored to peek at the top of the runqueue
+	struct sandbox *head_of_runqueue = sandbox_run_queue_remove();
+	uint64_t        local_deadline   = head_of_runqueue->absolute_deadline;
+	sandbox_run_queue_add(head_of_runqueue);
+
+	if (local_deadline <= global_deadline) {
+		return head_of_runqueue;
+	} else {
+		sandbox_request_t *sandbox_request = sandbox_request_scheduler_remove();
+		struct sandbox *   sandbox         = sandbox_allocate(sandbox_request);
+		assert(sandbox);
+		free(sandbox_request);
+		sandbox->state = RUNNABLE;
+		sandbox_run_queue_add(sandbox);
+		debuglog("[%p: %s]\n", sandbox, sandbox->module->name);
+		return sandbox;
+	}
+}
+
+
 uint64_t
 sandbox_get_priority(void *element)
 {
@@ -63,7 +119,8 @@ sandbox_run_queue_ps_initialize()
 	sandbox_run_queue_config_t config = { .add      = sandbox_run_queue_ps_add,
 		                              .is_empty = sandbox_run_queue_ps_is_empty,
 		                              .remove   = sandbox_run_queue_ps_remove,
-		                              .delete   = sandbox_run_queue_ps_delete };
+		                              .delete   = sandbox_run_queue_ps_delete,
+		                              .get_next = sandbox_run_queue_ps_get_next };
 
 	sandbox_run_queue_initialize(&config);
 }

runtime/src/software_interrupt.c

@@ -13,12 +13,14 @@
 #include <arch/context.h>
 #include <software_interrupt.h>
 #include <current_sandbox.h>
+#include "sandbox_run_queue.h"
 
 /***************************************
  * Process Globals
  ***************************************/
 
 static const int software_interrupt_supported_signals[] = { SIGALRM, SIGUSR1 };
+uint64_t         SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_CYCLES;
 
 /***************************************
  * Thread Globals
@@ -116,29 +118,31 @@ static inline void
 software_interrupt_schedule_alarm(void *user_context_raw)
 {
 	software_interrupt_disable(); // no nesting!
-
 	struct sandbox *current_sandbox                  = current_sandbox_get();
+	bool            should_enable_software_interrupt = true;
 
 	// If current_sandbox is null, there's nothing to preempt, so let the "main" scheduler run its course.
 	if (current_sandbox != NULL) {
-		// find a next sandbox to run..
-		struct sandbox *next_sandbox = worker_thread_get_next_sandbox();
+		struct sandbox *next_sandbox = sandbox_run_queue_get_next();
 
 		if (next_sandbox != NULL && next_sandbox != current_sandbox) {
 			ucontext_t *user_context = (ucontext_t *)user_context_raw;
 
-			// Save context to the sandbox we're switching from
+			// Save the context of the currently executing sandbox before switching from it
 			arch_mcontext_save(&current_sandbox->ctxt, &user_context->uc_mcontext);
 
-			// current_sandbox_set on it. restore through *user_context..
+			// Update current_sandbox to the next sandbox
 			current_sandbox_set(next_sandbox);
-			if (arch_mcontext_restore(&user_context->uc_mcontext, &next_sandbox->ctxt)) goto skip;
+
+			// And load the context of this new sandbox
+			// RC of 1 indicates that sandbox was last in a user-level context switch state,
+			// so do not enable software interrupts.
+			if (arch_mcontext_restore(&user_context->uc_mcontext, &next_sandbox->ctxt) == 1)
+				should_enable_software_interrupt = false;
 		}
 	}
 
-	software_interrupt_enable();
-skip:
-	return;
+	if (should_enable_software_interrupt) software_interrupt_enable();
 }
 
 /***************************************

runtime/src/worker_thread.c

@@ -106,7 +106,7 @@ worker_thread_block_current_sandbox(void)
 	previous_sandbox->state = BLOCKED;
 
 	// Switch to the next sandbox
-	struct sandbox *next_sandbox = worker_thread_get_next_sandbox();
+	struct sandbox *next_sandbox = sandbox_run_queue_get_next();
 	debuglog("[%p: %next_sandbox, %p: %next_sandbox]\n", previous_sandbox, previous_sandbox->module->name,
 	         next_sandbox, next_sandbox ? next_sandbox->module->name : "");
 	software_interrupt_enable();
@@ -147,32 +147,6 @@ void __attribute__((noinline)) __attribute__((noreturn)) worker_thread_sandbox_s
 		;
 }
 
-/**
- * Pulls up to 1..n sandbox requests, allocates them as sandboxes, sets them as runnable and places them on the local
- * runqueue, and then frees the sandbox requests The batch size pulled at once is set by SANDBOX_PULL_BATCH_SIZE
- * @return the number of sandbox requests pulled
- */
-static inline int
-worker_thread_pull_and_process_sandbox_requests(void)
-{
-	int total_sandboxes_pulled = 0;
-
-	while (total_sandboxes_pulled < SANDBOX_PULL_BATCH_SIZE) {
-		sandbox_request_t *sandbox_request;
-		if ((sandbox_request = sandbox_request_scheduler_remove()) == NULL) break;
-		// Actually allocate the sandbox for the requests that we've pulled
-		struct sandbox *sandbox = sandbox_allocate(sandbox_request);
-		assert(sandbox);
-		free(sandbox_request);
-		// Set the sandbox as runnable and place on the local runqueue
-		sandbox->state = RUNNABLE;
-		sandbox_run_queue_add(sandbox);
-		total_sandboxes_pulled++;
-	}
-
-	return total_sandboxes_pulled;
-}
-
 /**
  * Run all outstanding events in the local thread's libuv event loop
  **/
@@ -188,28 +162,6 @@ worker_thread_execute_libuv_event_loop(void)
 	worker_thread_is_in_callback = false;
 }
 
-/**
- * Execute the sandbox at the head of the thread local runqueue
- * If the runqueue is empty, pull a fresh batch of sandbox requests, instantiate them, and then execute the new head
- * @return the sandbox to execute or NULL if none are available
- **/
-struct sandbox *
-worker_thread_get_next_sandbox()
-{
-	if (sandbox_run_queue_is_empty()) {
-		int sandboxes_pulled = worker_thread_pull_and_process_sandbox_requests();
-		if (sandboxes_pulled == 0) return NULL;
-	}
-
-	// Execute Round Robin Scheduling Logic
-	struct sandbox *next_sandbox = sandbox_run_queue_remove();
-	assert(next_sandbox->state != RETURNED);
-	sandbox_run_queue_add(next_sandbox);
-
-	debuglog("[%p: %s]\n", next_sandbox, next_sandbox->module->name);
-	return next_sandbox;
-}
-
 /**
  * The entry function for sandbox worker threads
  * Initializes thread-local state, unmasks signals, sets up libuv loop and
@@ -221,8 +173,8 @@ worker_thread_main(void *return_code)
 	// Initialize Worker State
 	arch_context_init(&worker_thread_base_context, 0, 0);
 
-	// sandbox_run_queue_fifo_initialize();
-	sandbox_run_queue_ps_initialize();
+	sandbox_run_queue_fifo_initialize();
+	// sandbox_run_queue_ps_initialize();
 
 	sandbox_completion_queue_initialize();
 	software_interrupt_is_disabled = false;
@@ -243,7 +195,7 @@ worker_thread_main(void *return_code)
 		if (!worker_thread_is_in_callback) worker_thread_execute_libuv_event_loop();
 
 		software_interrupt_disable();
-		next_sandbox = worker_thread_get_next_sandbox();
+		next_sandbox = sandbox_run_queue_get_next();
 		software_interrupt_enable();
 
 		if (next_sandbox != NULL) {
@@ -272,7 +224,7 @@ worker_thread_exit_current_sandbox(void)
 	sandbox_run_queue_delete(previous_sandbox);
 	previous_sandbox->state = RETURNED;
 
-	struct sandbox *next_sandbox = worker_thread_get_next_sandbox();
+	struct sandbox *next_sandbox = sandbox_run_queue_get_next();
 	assert(next_sandbox != previous_sandbox);
 	software_interrupt_enable();
 	// Because the stack is still in use, only unmap linear memory and defer free resources until "main