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Date: Mon, 16 Mar 2020 16:02:23 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
Willem de Bruijn <willemb@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 3/3] net_sched: sch_fq: enable use of hrtimer slack
Add a new attribute to control the fq qdisc hrtimer slack.
Default is set to 10 usec.
When/if packets are throttled, fq set up an hrtimer that can
lead to one interrupt per packet in the throttled queue.
By using a timer slack, we allow better use of timer interrupts,
by giving them a chance to call multiple timer callbacks
at each hardware interrupt.
Also, giving a slack allows FQ to dequeue batches of packets
instead of a single one, thus increasing xmit_more efficiency.
This has no negative effect on the rate a TCP flow can sustain,
since each TCP flow maintains its own precise vtime (tp->tcp_wstamp_ns)
Tested:
1000 concurrent flows all using paced packets.
1,000,000 packets sent per second.
Before the patch :
$ vmstat 2 10
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 0 60726784 23628 3485992 0 0 138 1 977 535 0 12 87 0 0
0 0 0 60714700 23628 3485628 0 0 0 0 1568827 26462 0 22 78 0 0
1 0 0 60716012 23628 3485656 0 0 0 0 1570034 26216 0 22 78 0 0
0 0 0 60722420 23628 3485492 0 0 0 0 1567230 26424 0 22 78 0 0
0 0 0 60727484 23628 3485556 0 0 0 0 1568220 26200 0 22 78 0 0
2 0 0 60718900 23628 3485380 0 0 0 40 1564721 26630 0 22 78 0 0
2 0 0 60718096 23628 3485332 0 0 0 0 1562593 26432 0 22 78 0 0
0 0 0 60719608 23628 3485064 0 0 0 0 1563806 26238 0 22 78 0 0
1 0 0 60722876 23628 3485236 0 0 0 130 1565874 26566 0 22 78 0 0
1 0 0 60722752 23628 3484908 0 0 0 0 1567646 26247 0 22 78 0 0
After the patch, slack of 10 usec, we can see a reduction of interrupts
per second, and a small decrease of reported cpu usage.
$ vmstat 2 10
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
1 0 0 60722564 23628 3484728 0 0 133 1 696 545 0 13 87 0 0
1 0 0 60722568 23628 3484824 0 0 0 0 977278 25469 0 20 80 0 0
0 0 0 60716396 23628 3484764 0 0 0 0 979997 25326 0 20 80 0 0
0 0 0 60713844 23628 3484960 0 0 0 0 981394 25249 0 20 80 0 0
2 0 0 60720468 23628 3484916 0 0 0 0 982860 25062 0 20 80 0 0
1 0 0 60721236 23628 3484856 0 0 0 0 982867 25100 0 20 80 0 0
1 0 0 60722400 23628 3484456 0 0 0 8 982698 25303 0 20 80 0 0
0 0 0 60715396 23628 3484428 0 0 0 0 981777 25176 0 20 80 0 0
0 0 0 60716520 23628 3486544 0 0 0 36 978965 27857 0 21 79 0 0
0 0 0 60719592 23628 3486516 0 0 0 22 977318 25106 0 20 80 0 0
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
include/uapi/linux/pkt_sched.h | 2 ++
net/sched/sch_fq.c | 19 +++++++++++++++----
2 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index ea39287d59c812da7fc94379de41c2ba20e86557..7307a29a103e5191acd829c745860b637721be30 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -911,6 +911,8 @@ enum {
TCA_FQ_CE_THRESHOLD, /* DCTCP-like CE-marking threshold */
+ TCA_FQ_TIMER_SLACK, /* timer slack */
+
__TCA_FQ_MAX
};
diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 371ad84def3b6f1b5f0d0704b67723d0a8af22c6..9894577689faad16ed13c73725fb7da9b128bce9 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -121,6 +121,8 @@ struct fq_sched_data {
u64 stat_flows_plimit;
u64 stat_pkts_too_long;
u64 stat_allocation_errors;
+
+ u32 timer_slack; /* hrtimer slack in ns */
struct qdisc_watchdog watchdog;
};
@@ -504,8 +506,9 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
head = &q->old_flows;
if (!head->first) {
if (q->time_next_delayed_flow != ~0ULL)
- qdisc_watchdog_schedule_ns(&q->watchdog,
- q->time_next_delayed_flow);
+ qdisc_watchdog_schedule_range_ns(&q->watchdog,
+ q->time_next_delayed_flow,
+ q->timer_slack);
return NULL;
}
}
@@ -747,6 +750,7 @@ static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
[TCA_FQ_ORPHAN_MASK] = { .type = NLA_U32 },
[TCA_FQ_LOW_RATE_THRESHOLD] = { .type = NLA_U32 },
[TCA_FQ_CE_THRESHOLD] = { .type = NLA_U32 },
+ [TCA_FQ_TIMER_SLACK] = { .type = NLA_U32 },
};
static int fq_change(struct Qdisc *sch, struct nlattr *opt,
@@ -833,6 +837,9 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt,
q->ce_threshold = (u64)NSEC_PER_USEC *
nla_get_u32(tb[TCA_FQ_CE_THRESHOLD]);
+ if (tb[TCA_FQ_TIMER_SLACK])
+ q->timer_slack = nla_get_u32(tb[TCA_FQ_TIMER_SLACK]);
+
if (!err) {
sch_tree_unlock(sch);
err = fq_resize(sch, fq_log);
@@ -884,6 +891,8 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt,
q->orphan_mask = 1024 - 1;
q->low_rate_threshold = 550000 / 8;
+ q->timer_slack = 10 * NSEC_PER_USEC; /* 10 usec of hrtimer slack */
+
/* Default ce_threshold of 4294 seconds */
q->ce_threshold = (u64)NSEC_PER_USEC * ~0U;
@@ -924,7 +933,8 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
nla_put_u32(skb, TCA_FQ_LOW_RATE_THRESHOLD,
q->low_rate_threshold) ||
nla_put_u32(skb, TCA_FQ_CE_THRESHOLD, (u32)ce_threshold) ||
- nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log))
+ nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log) ||
+ nla_put_u32(skb, TCA_FQ_TIMER_SLACK, q->timer_slack))
goto nla_put_failure;
return nla_nest_end(skb, opts);
@@ -947,7 +957,8 @@ static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
st.flows_plimit = q->stat_flows_plimit;
st.pkts_too_long = q->stat_pkts_too_long;
st.allocation_errors = q->stat_allocation_errors;
- st.time_next_delayed_flow = q->time_next_delayed_flow - ktime_get_ns();
+ st.time_next_delayed_flow = q->time_next_delayed_flow + q->timer_slack -
+ ktime_get_ns();
st.flows = q->flows;
st.inactive_flows = q->inactive_flows;
st.throttled_flows = q->throttled_flows;
--
2.25.1.481.gfbce0eb801-goog
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