Hi Hillf,
Thanks for the patch.
I just tried it and it looks better than previous one. The issue
appeared only once over ~30 mins stressing (without the patch , it
shows up within 1 mins in usual, so I feel like we are getting close
to the final fix)
(pasted the modifications on my tree in case of any missing)
--- ./include/net/sch_generic.h.orig 2020-08-21 15:13:51.787952710 +0800
+++ ./include/net/sch_generic.h 2020-08-26 09:41:04.647173869 +0800
@@ -79,6 +79,7 @@
#define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump */
#define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
#define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
+ int pkt_seq;
u32 limit;
const struct Qdisc_ops *ops;
struct qdisc_size_table __rcu *stab;
--- ./include/net/pkt_sched.h.orig 2020-08-21 15:13:51.787952710 +0800
+++ ./include/net/pkt_sched.h 2020-08-26 09:42:14.491377514 +0800
@@ -117,8 +117,15 @@
static inline void qdisc_run(struct Qdisc *q)
{
if (qdisc_run_begin(q)) {
+ q->pkt_seq = 0;
+
__qdisc_run(q);
qdisc_run_end(q);
+
+ /* reschedule qdisc if there are packets enqueued */
+ if (q->pkt_seq != 0)
+ __netif_schedule(q);
+
}
}
--- ./net/core/dev.c.orig 2020-03-19 16:31:27.000000000 +0800
+++ ./net/core/dev.c 2020-08-26 09:47:57.783165885 +0800
@@ -2721,6 +2721,7 @@
local_irq_save(flags);
sd = this_cpu_ptr(&softnet_data);
+ q->pkt_seq = 0;
q->next_sched = NULL;
*sd->output_queue_tailp = q;
sd->output_queue_tailp = &q->next_sched;
--- ./net/sched/sch_generic.c.orig 2020-08-24 22:02:04.589830751 +0800
+++ ./net/sched/sch_generic.c 2020-08-26 09:43:40.987852551 +0800
@@ -403,6 +403,9 @@
*/
quota -= packets;
if (quota <= 0 || need_resched()) {
+ /* info caller to reschedule qdisc outside q->seqlock */
+ q->pkt_seq = 1;
+
__netif_schedule(q);
break;
}
Hillf Danton <hdan...@sina.com> 于2020年8月26日周三 上午12:26写道：
>
>
> Hi Feng,
>
> On Tue, 25 Aug 2020 15:14:12 +0800 Fengkehuan Feng wrote:
> > Hi Hillf,
> >
> > I just tried the updated version and the system can boot up now.
>
> Thanks again for your testing.
>
> > It does mitigate the issue a lot but still couldn't get rid of it
> > thoroughly. It seems to me like the effect of Cong's patch.
>
> Your echoes show we're still march in the dark and let's try another
> direction in which qdisc is rescheduled outside seqlock to make sure
> tx softirq is raised when there're more packets on the pfifo_fast to
> be transmitted.
>
> CPU0 CPU1
> ---- ----
> seqlock
> test __QDISC_STATE_SCHED
> raise tx softirq
> clear __QDISC_STATE_SCHED
> try seqlock
> __qdisc_run(q);
> sequnlock
> sequnlock
>
>
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -79,6 +79,7 @@ struct Qdisc {
> #define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump
> */
> #define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
> #define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
> + int pkt_seq;
> u32 limit;
> const struct Qdisc_ops *ops;
> struct qdisc_size_table __rcu *stab;
> --- a/include/net/pkt_sched.h
> +++ b/include/net/pkt_sched.h
> @@ -118,6 +118,8 @@ void __qdisc_run(struct Qdisc *q);
> static inline void qdisc_run(struct Qdisc *q)
> {
> if (qdisc_run_begin(q)) {
> + q->pkt_seq = 0;
> +
> /* NOLOCK qdisc must check 'state' under the qdisc seqlock
> * to avoid racing with dev_qdisc_reset()
> */
> @@ -125,6 +127,10 @@ static inline void qdisc_run(struct Qdis
> likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
> __qdisc_run(q);
> qdisc_run_end(q);
> +
> + /* reschedule qdisc if there are packets enqueued */
> + if (q->pkt_seq != 0)
> + __netif_schedule(q);
> }
> }
>
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -384,6 +384,8 @@ void __qdisc_run(struct Qdisc *q)
> while (qdisc_restart(q, &packets)) {
> quota -= packets;
> if (quota <= 0) {
> + /* info caller to reschedule qdisc outside q->seqlock
> */
> + q->pkt_seq = 1;
> __netif_schedule(q);
> break;
> }
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3031,6 +3031,7 @@ static void __netif_reschedule(struct Qd
>
> local_irq_save(flags);
> sd = this_cpu_ptr(&softnet_data);
> + q->pkt_seq = 0;
> q->next_sched = NULL;
> *sd->output_queue_tailp = q;
> sd->output_queue_tailp = &q->next_sched;
> --
>
