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authorAhmed S. Darwish <a.darwish@linutronix.de>2021-10-16 10:49:10 +0200
committerDavid S. Miller <davem@davemloft.net>2021-10-18 12:54:41 +0100
commit29cbcd85828372333aa87542c51f2b2b0fd4380c (patch)
tree6feb3ee12123611d1988813e9e139c4c81280aec /net/sched/sch_mq.c
parent50dc9a8572aa4d7cdc56670228fcde40289ed289 (diff)
net: sched: Remove Qdisc::running sequence counter
The Qdisc::running sequence counter has two uses: 1. Reliably reading qdisc's tc statistics while the qdisc is running (a seqcount read/retry loop at gnet_stats_add_basic()). 2. As a flag, indicating whether the qdisc in question is running (without any retry loops). For the first usage, the Qdisc::running sequence counter write section, qdisc_run_begin() => qdisc_run_end(), covers a much wider area than what is actually needed: the raw qdisc's bstats update. A u64_stats sync point was thus introduced (in previous commits) inside the bstats structure itself. A local u64_stats write section is then started and stopped for the bstats updates. Use that u64_stats sync point mechanism for the bstats read/retry loop at gnet_stats_add_basic(). For the second qdisc->running usage, a __QDISC_STATE_RUNNING bit flag, accessed with atomic bitops, is sufficient. Using a bit flag instead of a sequence counter at qdisc_run_begin/end() and qdisc_is_running() leads to the SMP barriers implicitly added through raw_read_seqcount() and write_seqcount_begin/end() getting removed. All call sites have been surveyed though, and no required ordering was identified. Now that the qdisc->running sequence counter is no longer used, remove it. Note, using u64_stats implies no sequence counter protection for 64-bit architectures. This can lead to the qdisc tc statistics "packets" vs. "bytes" values getting out of sync on rare occasions. The individual values will still be valid. Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched/sch_mq.c')
-rw-r--r--net/sched/sch_mq.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/net/sched/sch_mq.c b/net/sched/sch_mq.c
index cedd0b3ef9cf..83d2e54bf303 100644
--- a/net/sched/sch_mq.c
+++ b/net/sched/sch_mq.c
@@ -144,8 +144,8 @@ static int mq_dump(struct Qdisc *sch, struct sk_buff *skb)
qdisc = netdev_get_tx_queue(dev, ntx)->qdisc_sleeping;
spin_lock_bh(qdisc_lock(qdisc));
- gnet_stats_add_basic(NULL, &sch->bstats, qdisc->cpu_bstats,
- &qdisc->bstats);
+ gnet_stats_add_basic(&sch->bstats, qdisc->cpu_bstats,
+ &qdisc->bstats, false);
gnet_stats_add_queue(&sch->qstats, qdisc->cpu_qstats,
&qdisc->qstats);
sch->q.qlen += qdisc_qlen(qdisc);
@@ -231,8 +231,7 @@ static int mq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
struct netdev_queue *dev_queue = mq_queue_get(sch, cl);
sch = dev_queue->qdisc_sleeping;
- if (gnet_stats_copy_basic(&sch->running, d, sch->cpu_bstats,
- &sch->bstats) < 0 ||
+ if (gnet_stats_copy_basic(d, sch->cpu_bstats, &sch->bstats, true) < 0 ||
qdisc_qstats_copy(d, sch) < 0)
return -1;
return 0;