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| author | Ahmed S. Darwish <a.darwish@linutronix.de> | 2021-10-16 11:49:07 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2021-10-18 14:54:41 +0300 |
| commit | 67c9e6270f3013e4d86ec57c4e7f27459f2a0652 (patch) | |
| tree | 69cab1b15c62cd3dd449820ceebdd18107114c68 /net/sched/sch_generic.c | |
| parent | f2efdb17928924c9c935c136dea764a081032006 (diff) | |
| download | linux-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.c | 1 |
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) { |