Merge pull request #201 from gwsystems/dynamic-preemption-toggle

feat: make preemption toggle runtime config

runtime/Makefile

@@ -85,9 +85,6 @@ CFLAGS += -D${ARCH}
 CFLAGS += -DNCORES=${TOTAL_CORES}
 CFLAGS += -DPAGE_SIZE=$(PAGE_SIZE)
 
-# Optionally Disable preemption
-# CFLAGS += -DPREEMPT_DISABLE
-
 # Sandboxes running on Sledge always use WebAssembly linear memory
 CFLAGS += -DUSE_MEM_VM
 

runtime/experiments/bash_libraries/panic.sh

@@ -10,7 +10,7 @@ __common_dump_callstack() {
 	echo "Call Stack:"
 	# Skip the dump_bash_stack and error_msg_frames
 	for ((i = 2; i < ${#FUNCNAME[@]}; i++)); do
-		printf "\t%d - %s\n" "$((i - 2))" "${FUNCNAME[i]} (${BASH_SOURCE[i + 1]}:${BASH_LINENO[i]})"
+		printf "\t%d - %s\n" "$((i - 2))" "${FUNCNAME[i]} (${BASH_SOURCE[i + 1]}:${BASH_LINENO[i + 1]})"
 	done
 }
 

runtime/include/runtime.h

@@ -90,3 +90,5 @@ print_runtime_scheduler(enum RUNTIME_SCHEDULER variant)
 };
 
 extern enum RUNTIME_SCHEDULER runtime_scheduler;
+extern bool                   runtime_preemption_enabled;
+extern uint32_t               runtime_quantum_us;

runtime/include/software_interrupt.h

@@ -11,9 +11,6 @@
 
 #include "debuglog.h"
 
-#define SOFTWARE_INTERRUPT_TIME_TO_START_IN_USEC     (2 * 1000) /* 2 ms */
-#define SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_USEC (1 * 1000) /* 1 ms */
-
 /************
  * Externs  *
  ***********/

runtime/src/main.c

@@ -40,6 +40,10 @@ FILE *runtime_sandbox_perf_log = NULL;
 enum RUNTIME_SCHEDULER runtime_scheduler = RUNTIME_SCHEDULER_FIFO;
 int                    runtime_worker_core_count;
 
+
+bool     runtime_preemption_enabled = true;
+uint32_t runtime_quantum_us         = 5000; /* 5ms */
+
 /**
  * Returns instructions on use of CLI if used incorrectly
  * @param cmd - The command the user entered
@@ -213,6 +217,22 @@ runtime_configure()
 	}
 	printf("\tScheduler Policy: %s\n", print_runtime_scheduler(runtime_scheduler));
 
+	/* Runtime Preemption Toggle */
+	char *preempt_disable = getenv("SLEDGE_DISABLE_PREEMPTION");
+	if (preempt_disable != NULL && strcmp(preempt_disable, "false") != 0) runtime_preemption_enabled = false;
+	printf("\tPreemption: %s\n", runtime_preemption_enabled ? "Enabled" : "Disabled");
+
+	/* Runtime Quantum */
+	char *quantum_raw = getenv("SLEDGE_QUANTUM_US");
+	if (quantum_raw != NULL) {
+		long quantum = atoi(quantum_raw);
+		if (unlikely(quantum <= 0)) panic("SLEDGE_QUANTUM_US must be a positive integer, saw %ld\n", quantum);
+		if (unlikely(quantum > 999999))
+			panic("SLEDGE_QUANTUM_US must be less than 999999 ms, saw %ld\n", quantum);
+		runtime_quantum_us = (uint32_t)quantum;
+	}
+	printf("\tQuantum: %u us\n", runtime_quantum_us);
+
 	/* Runtime Perf Log */
 	char *runtime_sandbox_perf_log_path = getenv("SLEDGE_SANDBOX_PERF_LOG");
 	if (runtime_sandbox_perf_log_path != NULL) {
@@ -352,8 +372,7 @@ main(int argc, char **argv)
 	runtime_processor_speed_MHz = runtime_get_processor_speed_MHz();
 	if (unlikely(runtime_processor_speed_MHz == 0)) panic("Failed to detect processor speed\n");
 
-	software_interrupt_interval_duration_in_cycles = (uint64_t)SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_USEC
+	software_interrupt_interval_duration_in_cycles = (uint64_t)runtime_quantum_us * runtime_processor_speed_MHz;
-	                                                 * runtime_processor_speed_MHz;
 	printf("\tProcessor Speed: %u MHz\n", runtime_processor_speed_MHz);
 
 	runtime_set_resource_limits_to_max();

runtime/src/software_interrupt.c

@@ -165,9 +165,9 @@ software_interrupt_validate_worker()
 static inline void
 software_interrupt_handle_signals(int signal_type, siginfo_t *signal_info, void *user_context_raw)
 {
-#ifdef PREEMPT_DISABLE
+	if (unlikely(!runtime_preemption_enabled)) {
-	panic("Unexpectedly invoked signal handlers when PREEMPT_DISABLE set\n");
+		panic("Unexpectedly invoked signal handlers with preemption disabled\n");
-#else
+	}
 
 	software_interrupt_validate_worker();
 
@@ -190,7 +190,6 @@ software_interrupt_handle_signals(int signal_type, siginfo_t *signal_info, void
 		}
 	}
 	}
-#endif
 }
 
 /********************
@@ -198,24 +197,24 @@ software_interrupt_handle_signals(int signal_type, siginfo_t *signal_info, void
  *******************/
 
 /**
- * Arms the Interval Timer to start in 10ms and then trigger a SIGALRM every 5ms
+ * Arms the Interval Timer to start in one quantum and then trigger a SIGALRM every quantum
  */
 void
 software_interrupt_arm_timer(void)
 {
-#ifndef PREEMPT_DISABLE
+	if (!runtime_preemption_enabled) return;
+
 	struct itimerval interval_timer;
 
 	memset(&interval_timer, 0, sizeof(struct itimerval));
-	interval_timer.it_value.tv_usec    = SOFTWARE_INTERRUPT_TIME_TO_START_IN_USEC;
+	interval_timer.it_value.tv_usec    = runtime_quantum_us;
-	interval_timer.it_interval.tv_usec = SOFTWARE_INTERRUPT_INTERVAL_DURATION_IN_USEC;
+	interval_timer.it_interval.tv_usec = runtime_quantum_us;
 
 	int return_code = setitimer(ITIMER_REAL, &interval_timer, NULL);
 	if (return_code) {
 		perror("setitimer");
 		exit(1);
 	}
-#endif
 }
 
 /**

runtime/src/worker_thread.c

@@ -317,10 +317,11 @@ worker_thread_main(void *return_code)
 
 
 	/* Unmask signals */
-#ifndef PREEMPT_DISABLE
+	if (runtime_preemption_enabled) {
-	software_interrupt_unmask_signal(SIGALRM);
+		software_interrupt_unmask_signal(SIGALRM);
-	software_interrupt_unmask_signal(SIGUSR1);
+		software_interrupt_unmask_signal(SIGUSR1);
-#endif
+	}
+
 	signal(SIGPIPE, SIG_IGN);
 
 	/* Initialize epoll */