timer: apply PIT quirk to avoid high cpu load

repos/os/src/drivers/timer/include_pit/platform_timer.h

@@ -179,6 +179,37 @@ class Platform_timer
 			if (timeout_usec > max_timeout())
 				timeout_usec = max_timeout();
 
+			/*
+			 * XXX Quirk - start
+			 *
+			 * On some x86 platforms, it happens that the system seems to slow
+			 * down dramatically for some unclear reasons so far. When this
+			 * happens, the handling of the timeout queue and reprogramming the
+			 * next timeout takes so long that the timer IRQ will fire
+			 * immediately after acknowledging it. This causes the timer
+			 * service to run on a very high rate, which may utilize the CPU
+			 * close to the maximum. We try to detect this condition by the
+			 * following heuristic and apply this quirk, which programs the
+			 * next timeout later in time - so that it will fire not
+			 * immediately after acknowledging it.
+			 *
+			 * This quirk should be removed as soon as it is clear what
+			 * triggers the phenomenon.
+			 */
+			enum { QUIRK_TIMEOUT_US = 2800 };
+
+			unsigned long now   = curr_time();
+			asm volatile ("":::"memory");
+			unsigned long later = curr_time();
+
+			unsigned long diff = later - now;
+			if (diff > QUIRK_TIMEOUT_US) {
+				timeout_usec = diff * 6 > max_timeout() ? max_timeout() : diff * 6;
+				PERR("apply timer quirk - diff=%lu, timeout_usec=%lu",
+					 diff, timeout_usec);
+			}
+			/* XXX Quirk - end */
+
 			_counter_init_value = (PIT_TICKS_PER_MSEC * timeout_usec)/1000;
 			_set_counter(_counter_init_value);
 		}