+#define PIE_DEFAULT_QUEUE_LIMIT 200	/* in packets */
+#define QUEUE_THRESHOLD (5000)
+#define DQCOUNT_INVALID -1
+#define THRESHOLD_PKT_SIZE	1500
+#define MAX_INT_VALUE  0xffffffff
+#define MAX_INT_VALUE_CAP  (0xffffffff >> 8)

The above 2 constants are both unsigned (unless 'int' is larger than 32 bits).
If nothing else this means that they are very badly named.

+
+typedef u32 pie_time_t;
+typedef s32 pie_tdiff_t;
+#define PIE_SHIFT 10
+#define MS2PIETIME(a) ((a * NSEC_PER_MSEC) >> PIE_SHIFT)
+#define PIE_TIME_PER_SEC  ((NSEC_PER_SEC >> PIE_SHIFT))
+
+static inline pie_time_t pie_get_time(void)
+{
+	u64 ns = ktime_to_ns(ktime_get());
+	return ns >> PIE_SHIFT;
+}
+
+static inline u32 pie_time_to_ms(pie_time_t val)
+{
+	u64 valms = ((u64) val << PIE_SHIFT);
+
+	do_div(valms, NSEC_PER_MSEC);
+	return (u32) valms;
+}

There seems to be a lot of conversions between 1/1000 ms and 1/1024 ms.
On 32 bit systems they are horrid.
Not only that the conversions are open coded a lot of times as well.
It might also be better replacing '(val * 1000u) >> 10' with
'(val * (u64)(1000 << (32 - 10))) >> 32' since I'm not sure the compiler
will perform that substitution.

What happens if pie_time_to_ms() overflows 32 bits?
If it is only ever called for small values, there may be no need for
64bit maths at all.

...

+	if (delta > (s32) (MAX_INT_VALUE * 2 / 100)
+	    && q->vars.prob >= MAX_INT_VALUE / 10) {
+		delta = MAX_INT_VALUE * 2 / 100;

Calculating 'MAX_INT_VALUE * 2' isn't a good idea!
Whatever value it is supposed to be, it should be a named constant.

	David