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authorAhmed S. Darwish <a.darwish@linutronix.de>2021-10-16 11:49:07 +0300
committerDavid S. Miller <davem@davemloft.net>2021-10-18 14:54:41 +0300
commit67c9e6270f3013e4d86ec57c4e7f27459f2a0652 (patch)
tree69cab1b15c62cd3dd449820ceebdd18107114c68 /net/sched/sch_generic.c
parentf2efdb17928924c9c935c136dea764a081032006 (diff)
downloadlinux-67c9e6270f3013e4d86ec57c4e7f27459f2a0652.tar.xz
net: sched: Protect Qdisc::bstats with u64_stats
The not-per-CPU variant of qdisc tc (traffic control) statistics, Qdisc::gnet_stats_basic_packed bstats, is protected with Qdisc::running sequence counter. This sequence counter is used for reliably protecting bstats reads from parallel writes. Meanwhile, the seqcount's write section covers a much wider area than bstats update: qdisc_run_begin() => qdisc_run_end(). That read/write section asymmetry can lead to needless retries of the read section. To prepare for removing the Qdisc::running sequence counter altogether, introduce a u64_stats sync point inside bstats instead. Modify _bstats_update() to start/end the bstats u64_stats write section. For bisectability, and finer commits granularity, the bstats read section is still protected with a Qdisc::running read/retry loop and qdisc_run_begin/end() still starts/ends that seqcount write section. Once all call sites are modified to use _bstats_update(), the Qdisc::running seqcount will be removed and bstats read/retry loop will be modified to utilize the internal u64_stats sync point. Note, using u64_stats implies no sequence counter protection for 64-bit architectures. This can lead to the statistics "packets" vs. "bytes" values getting out of sync on rare occasions. The individual values will still be valid. [bigeasy: Minor commit message edits, init all gnet_stats_basic_packed.] 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_generic.c')
-rw-r--r--net/sched/sch_generic.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 8c64a552a64f..ef27ff3ddee4 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -892,6 +892,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
__skb_queue_head_init(&sch->gso_skb);
__skb_queue_head_init(&sch->skb_bad_txq);
qdisc_skb_head_init(&sch->q);
+ gnet_stats_basic_packed_init(&sch->bstats);
spin_lock_init(&sch->q.lock);
if (ops->static_flags & TCQ_F_CPUSTATS) {