From 1336c6a0ff4a291dbc7354bed5c0b0b89f54ae01 Mon Sep 17 00:00:00 2001
From: Matt Borgerson <contact@mborgerson.com>
Date: Tue, 2 Mar 2021 02:18:16 -0700
Subject: [PATCH] util/qemu-timer: Busy-wait in poll to prioritize timer
 deadlines

---
 util/qemu-timer.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/util/qemu-timer.c b/util/qemu-timer.c
index f62b4feecd..b04448a431 100644
--- a/util/qemu-timer.c
+++ b/util/qemu-timer.c
@@ -347,6 +347,22 @@ int qemu_poll_ns(GPollFD *fds, guint nfds, int64_t timeout)
         return ppoll((struct pollfd *)fds, nfds, &ts, NULL);
     }
 #else
+
+#ifdef XBOX
+    /* Timers are facilitated by this function. Busy-wait if the deadline is
+     * near, to avoid missing deadlines due to costly sleeps.
+     */
+    #define XBOX_BUSYWAIT_THRESHOLD_NS 1250000
+    if ((0 < timeout) && (timeout < XBOX_BUSYWAIT_THRESHOLD_NS)) {
+        int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+        int64_t end = now + timeout;
+        while (now < end) {
+            now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+        }
+        timeout = 0;
+    }
+#endif
+
     return g_poll(fds, nfds, qemu_timeout_ns_to_ms(timeout));
 #endif
 }