Get number of harts at runtime

Author: Mes0903

Makefile

@@ -78,7 +78,6 @@ E :=
 S := $E $E
 
 SMP ?= 1
-CFLAGS += -D SEMU_SMP=$(SMP)
 CFLAGS += -D SEMU_BOOT_TARGET_TIME=10
 .PHONY: riscv-harts.dtsi
 riscv-harts.dtsi:

main.c

@@ -619,7 +619,7 @@ static int semu_start(int argc, char **argv)
     emu.disk = virtio_blk_init(&(emu.vblk), disk_file);
 #endif
     /* Set up ACLINT */
-    semu_timer_init(&emu.mtimer.mtime, CLOCK_FREQ);
+    semu_timer_init(&emu.mtimer.mtime, CLOCK_FREQ, hart_count);
     emu.mtimer.mtimecmp = calloc(vm.n_hart, sizeof(uint64_t));
     emu.mswi.msip = calloc(vm.n_hart, sizeof(uint32_t));
     emu.sswi.ssip = calloc(vm.n_hart, sizeof(uint32_t));

utils.c

@@ -75,7 +75,7 @@ static inline uint64_t host_time_ns()
  *    'scale_factor' so the entire boot completes in SEMU_BOOT_TARGET_TIME
  *    seconds.
  */
-static void measure_bogomips_ns(uint64_t iterations)
+static void measure_bogomips_ns(uint64_t iterations, int hart_count)
 {
     /* Perform 'iterations' times calling the host HRT.
      *
@@ -114,13 +114,14 @@ static void measure_bogomips_ns(uint64_t iterations)
         (double) (elapsed_ns_2 - elapsed_ns_1) / (double) iterations;
 
     /* 'semu_timer_clocksource' is called ~2e8 times per SMP. Each call's
-     * overhead ~ ns_per_call. The total overhead is ~ ns_per_call * SMP * 2e8.
-     * That overhead is about 10% of the entire boot, so effectively:
+     * overhead ~ ns_per_call. The total overhead is ~ ns_per_call * SMP *
+     * 2e8. That overhead is about 10~40% of the entire boot, we take the
+     * minimum here to get more fault tolerance. Thus, effectively:
      *   predict_sec = ns_per_call * SMP * 2e8 * (100%/10%) / 1e9
      *               = ns_per_call * SMP * 2.0
      * Then scale_factor = (desired_time) / (predict_sec).
      */
-    const double predict_sec = ns_per_call * SEMU_SMP * 2.0;
+    const double predict_sec = ns_per_call * hart_count * 2.0;
     scale_factor = SEMU_BOOT_TARGET_TIME / predict_sec;
 }
 
@@ -188,14 +189,13 @@ static uint64_t semu_timer_clocksource(semu_timer_t *timer)
 #endif
 }
 
-void semu_timer_init(semu_timer_t *timer, uint64_t freq)
+void semu_timer_init(semu_timer_t *timer, uint64_t freq, int hart_count)
 {
     /* Measure how long each call to 'host_time_ns()' roughly takes,
      * then use that to pick 'scale_factor'. For example, pass freq
      * as the loop count or some large number to get a stable measure.
      */
-    measure_bogomips_ns(freq);
-
+    measure_bogomips_ns(freq, hart_count);
     timer->freq = freq;
     semu_timer_rebase(timer, 0);
 }

utils.h

@@ -11,6 +11,6 @@ typedef struct {
     uint64_t freq;
 } semu_timer_t;
 
-void semu_timer_init(semu_timer_t *timer, uint64_t freq);
+void semu_timer_init(semu_timer_t *timer, uint64_t freq, int hart_count);
 uint64_t semu_timer_get(semu_timer_t *timer);
 void semu_timer_rebase(semu_timer_t *timer, uint64_t time);