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-rw-r--r--net/sched/sch_pie.c21
1 files changed, 16 insertions, 5 deletions
diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index a255d0200a59..fefeeb73f15f 100644
--- 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 =
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