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authorAhmed S. Darwish <a.darwish@linutronix.de>2021-10-16 11:49:10 +0300
committerDavid S. Miller <davem@davemloft.net>2021-10-18 14:54:41 +0300
commit29cbcd85828372333aa87542c51f2b2b0fd4380c (patch)
tree6feb3ee12123611d1988813e9e139c4c81280aec /net/sched/sch_atm.c
parent50dc9a8572aa4d7cdc56670228fcde40289ed289 (diff)
downloadlinux-29cbcd85828372333aa87542c51f2b2b0fd4380c.tar.xz
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_atm.c')
-rw-r--r--net/sched/sch_atm.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/net/sched/sch_atm.c b/net/sched/sch_atm.c
index fbfe4ce9497b..4c8e994cf0a5 100644
--- a/net/sched/sch_atm.c
+++ b/net/sched/sch_atm.c
@@ -653,8 +653,7 @@ atm_tc_dump_class_stats(struct Qdisc *sch, unsigned long arg,
{
struct atm_flow_data *flow = (struct atm_flow_data *)arg;
- if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
- d, NULL, &flow->bstats) < 0 ||
+ if (gnet_stats_copy_basic(d, NULL, &flow->bstats, true) < 0 ||
gnet_stats_copy_queue(d, NULL, &flow->qstats, flow->q->q.qlen) < 0)
return -1;