net: sched: Cleanup PIE comments

[~andy/linux] / net / sched / sch_pie.c

diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index a255d0200a593a708a6f30f4e9dbb70fabb917c3..fefeeb73f15f18a84406ed686dc653ff3327ef45 100644 (file)
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c
@@ -15,6 +15,11 @@
  *
  * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
  * University of Oslo, Norway.
+ *
+ * References:
+ * IETF draft submission: http://tools.ietf.org/html/draft-pan-aqm-pie-00
+ * IEEE  Conference on High Performance Switching and Routing 2013 :
+ * "PIE: A * Lightweight Control Scheme to Address the Bufferbloat Problem"
  */
 
 #include <linux/module.h>
@@ -36,7 +41,7 @@ struct pie_params {
        psched_time_t target;   /* user specified target delay in pschedtime */
        u32 tupdate;            /* timer frequency (in jiffies) */
        u32 limit;              /* number of packets that can be enqueued */
-       u32 alpha;              /* alpha and beta are between -4 and 4 */
+       u32 alpha;              /* alpha and beta are between 0 and 32 */
        u32 beta;               /* and are used for shift relative to 1 */
        bool ecn;               /* true if ecn is enabled */
        bool bytemode;          /* to scale drop early prob based on pkt size */
@@ -326,10 +331,16 @@ static void calculate_probability(struct Qdisc *sch)
        if (qdelay == 0 && qlen != 0)
                update_prob = false;
 
-       /* Add ranges for alpha and beta, more aggressive for high dropping
-        * mode and gentle steps for light dropping mode
-        * In light dropping mode, take gentle steps; in medium dropping mode,
-        * take medium steps; in high dropping mode, take big steps.
+       /* In the algorithm, alpha and beta are between 0 and 2 with typical
+        * value for alpha as 0.125. In this implementation, we use values 0-32
+        * passed from user space to represent this. Also, alpha and beta have
+        * unit of HZ and need to be scaled before they can used to update
+        * probability. alpha/beta are updated locally below by 1) scaling them
+        * appropriately 2) scaling down by 16 to come to 0-2 range.
+        * Please see paper for details.
+        *
+        * We scale alpha and beta differently depending on whether we are in
+        * light, medium or high dropping mode.
         */
        if (q->vars.prob < MAX_PROB / 100) {
                alpha =