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net: sched: Cleanup PIE comments

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Fix incorrect comment reported by Norbert Kiesel. Edit another comment to add
more details. Also add references to algorithm (IETF draft and paper) to top of
file.

Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
CC: Mythili Prabhu <mysuryan@cisco.com>
CC: Norbert Kiesel <nkiesel@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vijay Subramanian 2014-02-12 18:58:21 -08:00 committed by David S. Miller
parent 89e101729b
commit 219e288e89
1 changed files with 16 additions and 5 deletions
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21
net/sched/sch_pie.c
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@ -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 =