| Message ID | 1524749556-36199-1-git-send-email-nogahf@mellanox.com |
|---|---|
| State | Rejected, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net-next] net: sch: prio: Set bands to default on delete instead of noop | expand |
On Thu, Apr 26, 2018 at 6:32 AM, Nogah Frankel <nogahf@mellanox.com> wrote: > When a band is created, it is set to the default qdisc, which is > "invisible" pfifo. Isn't TCA_DUMP_INVISIBLE for dumping this invisible qdisc? > However, if a band is set to a qdisc that is later being deleted, it will > be set to noop qdisc. This can cause a packet loss, while there is no clear > user indication for it. ("invisible" qdisc are not being shown by default). > This patch sets a band to the default qdisc, rather then the noop qdisc, on > delete operation. It is set to noop historically, may be not reasonable but changing it could break things. What's wrong with using TCA_DUMP_INVISIBLE to dump it?
From: Nogah Frankel <nogahf@mellanox.com> Date: Thu, 26 Apr 2018 16:32:36 +0300 > When a band is created, it is set to the default qdisc, which is > "invisible" pfifo. > However, if a band is set to a qdisc that is later being deleted, it will > be set to noop qdisc. This can cause a packet loss, while there is no clear > user indication for it. ("invisible" qdisc are not being shown by default). > This patch sets a band to the default qdisc, rather then the noop qdisc, on > delete operation. > > Signed-off-by: Nogah Frankel <nogahf@mellanox.com> Like Cong, I'm worried this will break something. The code has behaved this way for 2 decades or longer. If you want to put another qdisc there, and thus not drop any traffic, modify the qdisc to a new one instead of performing a delete operation.
> > When a band is created, it is set to the default qdisc, which is > > "invisible" pfifo. > > However, if a band is set to a qdisc that is later being deleted, it will > > be set to noop qdisc. This can cause a packet loss, while there is no clear > > user indication for it. ("invisible" qdisc are not being shown by default). > > This patch sets a band to the default qdisc, rather then the noop qdisc, on > > delete operation. > > > > Signed-off-by: Nogah Frankel <nogahf@mellanox.com> > > Like Cong, I'm worried this will break something. The code has > behaved this way for 2 decades or longer. > > If you want to put another qdisc there, and thus not drop any traffic, > modify the qdisc to a new one instead of performing a delete operation. I believe that this historic behavior is quite bug like, especially because TCA_DUMP_INVISIBLE is not set by default. Yet I accept your judgment that changing it now might break things. Thank you. Nogah
diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c index 222e53d..6862d23 100644 --- a/net/sched/sch_prio.c +++ b/net/sched/sch_prio.c @@ -314,8 +314,15 @@ static int prio_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new, bool any_qdisc_is_offloaded; int err; - if (new == NULL) - new = &noop_qdisc; + if (!new) { + new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops, + TC_H_MAKE(sch->handle, band + 1), + extack); + if (!new) + new = &noop_qdisc; + else + qdisc_hash_add(new, true); + } *old = qdisc_replace(sch, new, &q->queues[band]); @@ -332,7 +339,7 @@ static int prio_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new, &graft_offload); /* Don't report error if the graft is part of destroy operation. */ - if (err && new != &noop_qdisc) { + if (err && new->handle) { /* Don't report error if the parent, the old child and the new * one are not offloaded. */
When a band is created, it is set to the default qdisc, which is "invisible" pfifo. However, if a band is set to a qdisc that is later being deleted, it will be set to noop qdisc. This can cause a packet loss, while there is no clear user indication for it. ("invisible" qdisc are not being shown by default). This patch sets a band to the default qdisc, rather then the noop qdisc, on delete operation. Signed-off-by: Nogah Frankel <nogahf@mellanox.com> --- net/sched/sch_prio.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)