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| author |   Ahmed S. Darwish <a.darwish@linutronix.de> | 2021-10-16 10:49:07 +0200 |
|---|---|---|
| committer |   David S. Miller <davem@davemloft.net> | 2021-10-18 12:54:41 +0100 |
| commit | 67c9e6270f3013e4d86ec57c4e7f27459f2a0652 (patch) | |
| tree | 69cab1b15c62cd3dd449820ceebdd18107114c68 /include | |
| parent | u64_stats: Introduce u64_stats_set() (diff) | |
| download | linux-dev-67c9e6270f3013e4d86ec57c4e7f27459f2a0652.tar.xz linux-dev-67c9e6270f3013e4d86ec57c4e7f27459f2a0652.zip | |
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 'include')
| -rw-r--r-- | include/net/gen_stats.h | 2 | ||||
| -rw-r--r-- | include/net/sch_generic.h | 2 |
2 files changed, 4 insertions, 0 deletions
diff --git a/include/net/gen_stats.h b/include/net/gen_stats.h index d47155f5db5d..304d792f7977 100644 --- a/include/net/gen_stats.h +++ b/include/net/gen_stats.h @@ -11,6 +11,7 @@ struct gnet_stats_basic_packed { __u64 bytes; __u64 packets; + struct u64_stats_sync syncp; }; struct gnet_stats_basic_cpu { @@ -34,6 +35,7 @@ struct gnet_dump { struct tc_stats tc_stats; }; +void gnet_stats_basic_packed_init(struct gnet_stats_basic_packed *b); int gnet_stats_start_copy(struct sk_buff *skb, int type, spinlock_t *lock, struct gnet_dump *d, int padattr); diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 7bc2d30b5c06..d7746aea3cec 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -852,8 +852,10 @@ static inline int qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch, static inline void _bstats_update(struct gnet_stats_basic_packed *bstats, __u64 bytes, __u32 packets) { + u64_stats_update_begin(&bstats->syncp); bstats->bytes += bytes; bstats->packets += packets; + u64_stats_update_end(&bstats->syncp); } static inline void bstats_update(struct gnet_stats_basic_packed *bstats, |