chore: doubled checked input_handler lag measurements

Author: Gnarus-G

TWO_IMPLEMENTATIONS.md

@@ -16,7 +16,7 @@ that your mouse has.
 The new driver has general compatibility with the mice that linux already supports. 
 In exchange it has 'more' lag than the old driver. Inconsequentially more. See the plot.
 
-![Screenshot_2024-08-10_02-47-37](https://github.com/user-attachments/assets/def3a9d0-2bf3-401e-960c-b299592d1658)
+![Screenshot_2024-08-10_21-18-10](https://github.com/user-attachments/assets/2775d411-a3bb-40bc-a33d-b364debb3ed0)
 
 We're talking microseconds here, so you have no reason to use the old driver.
 If, for some reason, you want to use the old driver and it supports your mouse. You can bind to it like so:

bench/Makefile

@@ -1,19 +1,13 @@
 bench_driver: build
-	bin/evdriverlag
+	@bin/evdriverlag
 
 bench_handler: build
-	bin/evinputlag
+	@bin/evinputlag
 
-build: evdriverlag.o evinputlag.o
-	mkdir -p bin
-	cc evdriverlag.o -o bin/evdriverlag
-	cc evinputlag.o -o bin/evinputlag
-
-evdriverlag.o: evdriverlag.c
-	cc -c evdriverlag.c
-
-evinputlag.o: evinputlag.c
-	cc -c evinputlag.c
+build: evdriverlag.c evinputlag.c
+	@mkdir -p bin
+	@cc evdriverlag.c -o bin/evdriverlag
+	@cc evinputlag.c -o bin/evinputlag
 
 clean:
 	rm *.o

bench/evinputlag.c

@@ -4,9 +4,7 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#define MOUSE_DEVICE "/dev/input/event2"
-
-#define VIRTUAL_DEVICE "/dev/input/event9"
+#define VIRTUAL_DEVICE "/dev/input/event7"
 
 static __suseconds_t to_us(struct timeval time) {
   return time.tv_sec * 1000000L + time.tv_usec;
@@ -16,21 +14,16 @@ static __suseconds_t to_us(struct timeval time) {
 
 /**
  * NOTE: This benchmark depends on temporarily setting
- * maccel_filter from input_handler.h to return false
- * on EV_REL instead of true. So we can measure the original
- * event time from the physical device's event.
+ * maccel_filter from input_handler.h to inject ktime_t diff (in us)
+ * between when the original event was received and the modified event was
+ * reported, as the value of the REL_Z REL_ABS event. So we can measure the
+ * extra lag from the input_handler. Assuming REL_Z, REL_ABS are only produced
+ * as carriers of the extra lag measurement.
  *
  */
 
 int main(void) {
-  // Open the source device
-  int fd_source = open(MOUSE_DEVICE, O_RDONLY);
-  if (fd_source < 0) {
-    perror("Failed to open source device");
-    return 1;
-  }
-
-  int vfd_source = open(VIRTUAL_DEVICE, O_RDONLY);
+  int fd_source = open(VIRTUAL_DEVICE, O_RDONLY);
   if (fd_source < 0) {
     perror("Failed to open virtual device");
     return 1;
@@ -40,35 +33,36 @@ int main(void) {
   int tidx = 0;
 
   // Main loop to read, modify, and write events
-  struct input_event sev;
-  struct input_event vev;
-  while (tidx < EVENT_TIME_PAIR_CNT &&
-         read(vfd_source, &vev, sizeof(vev)) > 0) {
+  struct input_event ev;
+  while (tidx < EVENT_TIME_PAIR_CNT && read(fd_source, &ev, sizeof(ev)) > 0) {
     struct timeval now;
     gettimeofday(&now, NULL);
 
-    if (read(fd_source, &sev, sizeof(sev)) <= 0) {
-      break;
+    if (ev.type == EV_REL && (ev.code == 2 || ev.code == 3)) {
+      /* fprintf(stderr, "EVENT: type %d, code %d, value %d\n", ev.type,
+       * ev.code, */
+      /*         ev.value); */
+      times[tidx++] = to_us(ev.time);
+      times[tidx++] = to_us(now);
+      times[tidx++] = ev.value;
     }
-
-    times[tidx++] = to_us(sev.time);
-    times[tidx++] = to_us(vev.time);
-    times[tidx++] = to_us(now);
   }
 
   // Cleanup
   close(fd_source);
 
   tidx = 0;
 
-  printf("event_time,virtual_event_time,read_time,diff\n"); // eve'ry is in us
+  printf("event_time,read_time,naive_diff,extra_lag,diff\n"); // eve'ry is in us
   while (tidx < EVENT_TIME_PAIR_CNT) {
     __suseconds_t event_time = times[tidx++];
-    __suseconds_t virtual_event_time = times[tidx++];
     __suseconds_t read_time = times[tidx++];
+    __suseconds_t extra_lag_measured_by_input_handler = times[tidx++];
 
-    printf("%lu,%lu,%lu,%lu\n", event_time, virtual_event_time, read_time,
-           read_time - event_time);
+    __suseconds_t diff = read_time - event_time;
+    printf("%lu,%lu,%lu,%lu,%lu\n", event_time, read_time, diff,
+           extra_lag_measured_by_input_handler,
+           diff + extra_lag_measured_by_input_handler);
   }
 
   return 0;