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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_stats.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_stats.c')
-rw-r--r-- | net/core/gen_stats.c | 50 |
1 files changed, 28 insertions, 22 deletions
diff --git a/net/core/gen_stats.c b/net/core/gen_stats.c index 5f57f761def6..5516ea0d5da0 100644 --- a/net/core/gen_stats.c +++ b/net/core/gen_stats.c @@ -146,42 +146,42 @@ static void gnet_stats_add_basic_cpu(struct gnet_stats_basic_sync *bstats, _bstats_update(bstats, t_bytes, t_packets); } -void gnet_stats_add_basic(const seqcount_t *running, - struct gnet_stats_basic_sync *bstats, +void gnet_stats_add_basic(struct gnet_stats_basic_sync *bstats, struct gnet_stats_basic_sync __percpu *cpu, - struct gnet_stats_basic_sync *b) + struct gnet_stats_basic_sync *b, bool running) { - unsigned int seq; + unsigned int start; u64 bytes = 0; u64 packets = 0; + WARN_ON_ONCE((cpu || running) && !in_task()); + if (cpu) { gnet_stats_add_basic_cpu(bstats, cpu); return; } do { if (running) - seq = read_seqcount_begin(running); + start = u64_stats_fetch_begin_irq(&b->syncp); bytes = u64_stats_read(&b->bytes); packets = u64_stats_read(&b->packets); - } while (running && read_seqcount_retry(running, seq)); + } while (running && u64_stats_fetch_retry_irq(&b->syncp, start)); _bstats_update(bstats, bytes, packets); } EXPORT_SYMBOL(gnet_stats_add_basic); static int -___gnet_stats_copy_basic(const seqcount_t *running, - struct gnet_dump *d, +___gnet_stats_copy_basic(struct gnet_dump *d, struct gnet_stats_basic_sync __percpu *cpu, struct gnet_stats_basic_sync *b, - int type) + int type, bool running) { struct gnet_stats_basic_sync bstats; u64 bstats_bytes, bstats_packets; gnet_stats_basic_sync_init(&bstats); - gnet_stats_add_basic(running, &bstats, cpu, b); + gnet_stats_add_basic(&bstats, cpu, b, running); bstats_bytes = u64_stats_read(&bstats.bytes); bstats_packets = u64_stats_read(&bstats.packets); @@ -210,10 +210,14 @@ ___gnet_stats_copy_basic(const seqcount_t *running, /** * gnet_stats_copy_basic - copy basic statistics into statistic TLV - * @running: seqcount_t pointer * @d: dumping handle * @cpu: copy statistic per cpu * @b: basic statistics + * @running: true if @b represents a running qdisc, thus @b's + * internal values might change during basic reads. + * Only used if @cpu is NULL + * + * Context: task; must not be run from IRQ or BH contexts * * Appends the basic statistics to the top level TLV created by * gnet_stats_start_copy(). @@ -222,22 +226,25 @@ ___gnet_stats_copy_basic(const seqcount_t *running, * if the room in the socket buffer was not sufficient. */ int -gnet_stats_copy_basic(const seqcount_t *running, - struct gnet_dump *d, +gnet_stats_copy_basic(struct gnet_dump *d, struct gnet_stats_basic_sync __percpu *cpu, - struct gnet_stats_basic_sync *b) + struct gnet_stats_basic_sync *b, + bool running) { - return ___gnet_stats_copy_basic(running, d, cpu, b, - TCA_STATS_BASIC); + return ___gnet_stats_copy_basic(d, cpu, b, TCA_STATS_BASIC, running); } EXPORT_SYMBOL(gnet_stats_copy_basic); /** * gnet_stats_copy_basic_hw - copy basic hw statistics into statistic TLV - * @running: seqcount_t pointer * @d: dumping handle * @cpu: copy statistic per cpu * @b: basic statistics + * @running: true if @b represents a running qdisc, thus @b's + * internal values might change during basic reads. + * Only used if @cpu is NULL + * + * Context: task; must not be run from IRQ or BH contexts * * Appends the basic statistics to the top level TLV created by * gnet_stats_start_copy(). @@ -246,13 +253,12 @@ EXPORT_SYMBOL(gnet_stats_copy_basic); * if the room in the socket buffer was not sufficient. */ int -gnet_stats_copy_basic_hw(const seqcount_t *running, - struct gnet_dump *d, +gnet_stats_copy_basic_hw(struct gnet_dump *d, struct gnet_stats_basic_sync __percpu *cpu, - struct gnet_stats_basic_sync *b) + struct gnet_stats_basic_sync *b, + bool running) { - return ___gnet_stats_copy_basic(running, d, cpu, b, - TCA_STATS_BASIC_HW); + return ___gnet_stats_copy_basic(d, cpu, b, TCA_STATS_BASIC_HW, running); } EXPORT_SYMBOL(gnet_stats_copy_basic_hw); |