net_sched: sch_fq: enable use of hrtimer slack (583396f4) · Commits · 戴 / test

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) v2: added strict netlink checking (as feedback from Jakub Kicinski) 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@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/uapi/linux/pkt_sched.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -911,6 +911,8 @@ enum {

		TCA_FQ_CE_THRESHOLD, /* DCTCP-like CE-marking threshold */

		TCA_FQ_TIMER_SLACK, /* timer slack */

		__TCA_FQ_MAX
		};

net/sched/sch_fq.c

+17 −4

Original line number	Diff line number	Diff line
		@@ -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 @@ begin:
		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;
		}
		}
		@@ -735,6 +738,8 @@ static int fq_resize(struct Qdisc *sch, u32 log)
		}

		static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
		[TCA_FQ_UNSPEC] = { .strict_start_type = TCA_FQ_TIMER_SLACK },

		[TCA_FQ_PLIMIT] = { .type = NLA_U32 },
		[TCA_FQ_FLOW_PLIMIT] = { .type = NLA_U32 },
		[TCA_FQ_QUANTUM] = { .type = NLA_U32 },
		@@ -747,6 +752,7 @@ 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 +839,9 @@ 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 +893,8 @@ 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 +935,8 @@ 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 +959,8 @@ 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;

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