linux-stable/include/net/gen_stats.h
Ahmed S. Darwish 29cbcd8582 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>
2021-10-18 12:54:41 +01:00

84 lines
3 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __NET_GEN_STATS_H
#define __NET_GEN_STATS_H
#include <linux/gen_stats.h>
#include <linux/socket.h>
#include <linux/rtnetlink.h>
#include <linux/pkt_sched.h>
/* Throughput stats.
* Must be initialized beforehand with gnet_stats_basic_sync_init().
*
* If no reads can ever occur parallel to writes (e.g. stack-allocated
* bstats), then the internal stat values can be written to and read
* from directly. Otherwise, use _bstats_set/update() for writes and
* gnet_stats_add_basic() for reads.
*/
struct gnet_stats_basic_sync {
u64_stats_t bytes;
u64_stats_t packets;
struct u64_stats_sync syncp;
} __aligned(2 * sizeof(u64));
struct net_rate_estimator;
struct gnet_dump {
spinlock_t * lock;
struct sk_buff * skb;
struct nlattr * tail;
/* Backward compatibility */
int compat_tc_stats;
int compat_xstats;
int padattr;
void * xstats;
int xstats_len;
struct tc_stats tc_stats;
};
void gnet_stats_basic_sync_init(struct gnet_stats_basic_sync *b);
int gnet_stats_start_copy(struct sk_buff *skb, int type, spinlock_t *lock,
struct gnet_dump *d, int padattr);
int gnet_stats_start_copy_compat(struct sk_buff *skb, int type,
int tc_stats_type, int xstats_type,
spinlock_t *lock, struct gnet_dump *d,
int padattr);
int gnet_stats_copy_basic(struct gnet_dump *d,
struct gnet_stats_basic_sync __percpu *cpu,
struct gnet_stats_basic_sync *b, bool running);
void gnet_stats_add_basic(struct gnet_stats_basic_sync *bstats,
struct gnet_stats_basic_sync __percpu *cpu,
struct gnet_stats_basic_sync *b, bool running);
int gnet_stats_copy_basic_hw(struct gnet_dump *d,
struct gnet_stats_basic_sync __percpu *cpu,
struct gnet_stats_basic_sync *b, bool running);
int gnet_stats_copy_rate_est(struct gnet_dump *d,
struct net_rate_estimator __rcu **ptr);
int gnet_stats_copy_queue(struct gnet_dump *d,
struct gnet_stats_queue __percpu *cpu_q,
struct gnet_stats_queue *q, __u32 qlen);
void gnet_stats_add_queue(struct gnet_stats_queue *qstats,
const struct gnet_stats_queue __percpu *cpu_q,
const struct gnet_stats_queue *q);
int gnet_stats_copy_app(struct gnet_dump *d, void *st, int len);
int gnet_stats_finish_copy(struct gnet_dump *d);
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,
bool running, struct nlattr *opt);
void gen_kill_estimator(struct net_rate_estimator __rcu **ptr);
int gen_replace_estimator(struct gnet_stats_basic_sync *bstats,
struct gnet_stats_basic_sync __percpu *cpu_bstats,
struct net_rate_estimator __rcu **ptr,
spinlock_t *lock,
bool running, struct nlattr *opt);
bool gen_estimator_active(struct net_rate_estimator __rcu **ptr);
bool gen_estimator_read(struct net_rate_estimator __rcu **ptr,
struct gnet_stats_rate_est64 *sample);
#endif