This reverts commit d47a0ac7b6 (sch_sfq: dont put new flow at the end of flows) As Jesper found out, patch sounded great but has bad side effects. In stress situation, pushing new flows in front of the queue can prevent old flows doing any progress. Packets can stay in SFQ queue for unlimited amount of time. It's possible to add heuristics to limit this problem, but this would add complexity outside of SFQ scope. A more sensible answer to Dave Taht concerns (who reported the issued I tried to solve in original commit) is probably to use a qdisc hierarchy so that high prio packets dont enter a potentially crowded SFQ qdisc.
Unified · Split
| @@ -469,11 +469,15 @@ enqueue: · 468 unmodified lines | |||
| 469 | if (slot->qlen == 1) { /* The flow is new */ | 469 | if (slot->qlen == 1) { /* The flow is new */ |
| 470 | if (q->tail == NULL) { /* It is the first flow */ | 470 | if (q->tail == NULL) { /* It is the first flow */ |
| 471 | slot->next = x; | 471 | slot->next = x; |
| 472 | q->tail = slot; | ||
| 473 | } else { | 472 | } else { |
| 474 | slot->next = q->tail->next; | 473 | slot->next = q->tail->next; |
| 475 | q->tail->next = x; | 474 | q->tail->next = x; |
| 476 | } | 475 | } |
| 476 | /* We put this flow at the end of our flow list. | ||
| 477 | * This might sound unfair for a new flow to wait after old ones, | ||
| 478 | * but we could endup servicing new flows only, and freeze old ones. | ||
| 479 | */ | ||
| 480 | q->tail = slot; | ||
| 477 | /* We could use a bigger initial quantum for new flows */ | 481 | /* We could use a bigger initial quantum for new flows */ |
| 478 | slot->allot = q->scaled_quantum; | 482 | slot->allot = q->scaled_quantum; |
| 479 | } | 483 | } |