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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_drr.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_drr.c')
-rw-r--r--net/sched/sch_drr.c10
1 files changed, 3 insertions, 7 deletions
diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 7243617a3595..18e4f7a0b291 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -85,8 +85,7 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
if (tca[TCA_RATE]) {
err = gen_replace_estimator(&cl->bstats, NULL,
&cl->rate_est,
- NULL,
- qdisc_root_sleeping_running(sch),
+ NULL, true,
tca[TCA_RATE]);
if (err) {
NL_SET_ERR_MSG(extack, "Failed to replace estimator");
@@ -119,9 +118,7 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
if (tca[TCA_RATE]) {
err = gen_replace_estimator(&cl->bstats, NULL, &cl->rate_est,
- NULL,
- qdisc_root_sleeping_running(sch),
- tca[TCA_RATE]);
+ NULL, true, tca[TCA_RATE]);
if (err) {
NL_SET_ERR_MSG(extack, "Failed to replace estimator");
qdisc_put(cl->qdisc);
@@ -268,8 +265,7 @@ static int drr_dump_class_stats(struct Qdisc *sch, unsigned long arg,
if (qlen)
xstats.deficit = cl->deficit;
- if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
- d, NULL, &cl->bstats) < 0 ||
+ if (gnet_stats_copy_basic(d, NULL, &cl->bstats, true) < 0 ||
gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
gnet_stats_copy_queue(d, cl_q->cpu_qstats, &cl_q->qstats, qlen) < 0)
return -1;