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author | Ahmed S. Darwish <a.darwish@linutronix.de> | 2021-10-16 11:49:10 +0300 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2021-10-18 14:54:41 +0300 |
commit | 29cbcd85828372333aa87542c51f2b2b0fd4380c (patch) | |
tree | 6feb3ee12123611d1988813e9e139c4c81280aec /net/core/gen_estimator.c | |
parent | 50dc9a8572aa4d7cdc56670228fcde40289ed289 (diff) | |
download | linux-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/core/gen_estimator.c')
-rw-r--r-- | net/core/gen_estimator.c | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c index a73ad0bf324c..4fcbdd71c59f 100644 --- a/net/core/gen_estimator.c +++ b/net/core/gen_estimator.c @@ -42,7 +42,7 @@ struct net_rate_estimator { struct gnet_stats_basic_sync *bstats; spinlock_t *stats_lock; - seqcount_t *running; + bool running; struct gnet_stats_basic_sync __percpu *cpu_bstats; u8 ewma_log; u8 intvl_log; /* period : (250ms << intvl_log) */ @@ -66,7 +66,7 @@ static void est_fetch_counters(struct net_rate_estimator *e, if (e->stats_lock) spin_lock(e->stats_lock); - gnet_stats_add_basic(e->running, b, e->cpu_bstats, e->bstats); + gnet_stats_add_basic(b, e->cpu_bstats, e->bstats, e->running); if (e->stats_lock) spin_unlock(e->stats_lock); @@ -113,7 +113,9 @@ static void est_timer(struct timer_list *t) * @cpu_bstats: bstats per cpu * @rate_est: rate estimator statistics * @lock: lock for statistics and control path - * @running: qdisc running seqcount + * @running: true if @bstats represents a running qdisc, thus @bstats' + * internal values might change during basic reads. Only used + * if @bstats_cpu is NULL * @opt: rate estimator configuration TLV * * Creates a new rate estimator with &bstats as source and &rate_est @@ -129,7 +131,7 @@ int gen_new_estimator(struct gnet_stats_basic_sync *bstats, struct gnet_stats_basic_sync __percpu *cpu_bstats, struct net_rate_estimator __rcu **rate_est, spinlock_t *lock, - seqcount_t *running, + bool running, struct nlattr *opt) { struct gnet_estimator *parm = nla_data(opt); @@ -218,7 +220,9 @@ EXPORT_SYMBOL(gen_kill_estimator); * @cpu_bstats: bstats per cpu * @rate_est: rate estimator statistics * @lock: lock for statistics and control path - * @running: qdisc running seqcount (might be NULL) + * @running: true if @bstats represents a running qdisc, thus @bstats' + * internal values might change during basic reads. Only used + * if @cpu_bstats is NULL * @opt: rate estimator configuration TLV * * Replaces the configuration of a rate estimator by calling @@ -230,7 +234,7 @@ int gen_replace_estimator(struct gnet_stats_basic_sync *bstats, struct gnet_stats_basic_sync __percpu *cpu_bstats, struct net_rate_estimator __rcu **rate_est, spinlock_t *lock, - seqcount_t *running, struct nlattr *opt) + bool running, struct nlattr *opt) { return gen_new_estimator(bstats, cpu_bstats, rate_est, lock, running, opt); |