From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 14 Sep 2016 17:36:35 +0200
Subject: net/Qdisc: use a seqlock instead seqcount
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: ab477791f151d454602bd7d3c57d654403f97759
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension
The seqcount disables preemption on -RT while it is held which can't
remove. Also we don't want the reader to spin for ages if the writer is
scheduled out. The seqlock on the other hand will serialize / sleep on
the lock while writer is active.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
include/linux/seqlock.h | 9 +++++++++
include/net/gen_stats.h | 11 ++++++-----
include/net/net_seq_lock.h | 15 +++++++++++++++
include/net/sch_generic.h | 19 +++++++++++++++++--
net/core/gen_estimator.c | 6 +++---
net/core/gen_stats.c | 12 ++++++------
net/sched/sch_api.c | 2 +-
net/sched/sch_generic.c | 12 ++++++++++++
8 files changed, 69 insertions(+), 17 deletions(-)
create mode 100644 include/net/net_seq_lock.h
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 17a872117585..3d7223ffdd3b 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -481,6 +481,15 @@ static inline void write_seqlock(seqlock_t *sl)
__raw_write_seqcount_begin(&sl->seqcount);
}
+static inline int try_write_seqlock(seqlock_t *sl)
+{
+ if (spin_trylock(&sl->lock)) {
+ __raw_write_seqcount_begin(&sl->seqcount);
+ return 1;
+ }
+ return 0;
+}
+
static inline void write_sequnlock(seqlock_t *sl)
{
__raw_write_seqcount_end(&sl->seqcount);
diff --git a/include/net/gen_stats.h b/include/net/gen_stats.h
index afea89895713..8a5d0135d362 100644
--- a/include/net/gen_stats.h
+++ b/include/net/gen_stats.h
@@ -5,6 +5,7 @@
#include <linux/socket.h>
#include <linux/rtnetlink.h>
#include <linux/pkt_sched.h>
+#include <net/net_seq_lock.h>
struct gnet_stats_basic_cpu {
struct gnet_stats_basic_packed bstats;
@@ -35,15 +36,15 @@ int gnet_stats_start_copy_compat(struct sk_buff *skb, int type,
spinlock_t *lock, struct gnet_dump *d,
int padattr);
-int gnet_stats_copy_basic(const seqcount_t *running,
+int gnet_stats_copy_basic(net_seqlock_t *running,
struct gnet_dump *d,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b);
-void __gnet_stats_copy_basic(const seqcount_t *running,
+void __gnet_stats_copy_basic(net_seqlock_t *running,
struct gnet_stats_basic_packed *bstats,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b);
-int gnet_stats_copy_basic_hw(const seqcount_t *running,
+int gnet_stats_copy_basic_hw(net_seqlock_t *running,
struct gnet_dump *d,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b);
@@ -63,13 +64,13 @@ int gen_new_estimator(struct gnet_stats_basic_packed *bstats,
struct gnet_stats_basic_cpu __percpu *cpu_bstats,
struct net_rate_estimator __rcu **rate_est,
spinlock_t *lock,
- seqcount_t *running, struct nlattr *opt);
+ net_seqlock_t *running, struct nlattr *opt);
void gen_kill_estimator(struct net_rate_estimator __rcu **ptr);
int gen_replace_estimator(struct gnet_stats_basic_packed *bstats,
struct gnet_stats_basic_cpu __percpu *cpu_bstats,
struct net_rate_estimator __rcu **ptr,
spinlock_t *lock,
- seqcount_t *running, struct nlattr *opt);
+ net_seqlock_t *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);
diff --git a/include/net/net_seq_lock.h b/include/net/net_seq_lock.h
new file mode 100644
index 000000000000..a7034298a82a
--- /dev/null
+++ b/include/net/net_seq_lock.h
@@ -0,0 +1,15 @@
+#ifndef __NET_NET_SEQ_LOCK_H__
+#define __NET_NET_SEQ_LOCK_H__
+
+#ifdef CONFIG_PREEMPT_RT_BASE
+# define net_seqlock_t seqlock_t
+# define net_seq_begin(__r) read_seqbegin(__r)
+# define net_seq_retry(__r, __s) read_seqretry(__r, __s)
+
+#else
+# define net_seqlock_t seqcount_t
+# define net_seq_begin(__r) read_seqcount_begin(__r)
+# define net_seq_retry(__r, __s) read_seqcount_retry(__r, __s)
+#endif
+
+#endif
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 45e4ee119e5f..7c0d2d70369a 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -13,6 +13,7 @@
#include <linux/workqueue.h>
#include <net/gen_stats.h>
#include <net/rtnetlink.h>
+#include <net/net_seq_lock.h>
struct Qdisc_ops;
struct qdisc_walker;
@@ -98,7 +99,7 @@ struct Qdisc {
struct sk_buff_head gso_skb ____cacheline_aligned_in_smp;
struct qdisc_skb_head q;
struct gnet_stats_basic_packed bstats;
- seqcount_t running;
+ net_seqlock_t running;
struct gnet_stats_queue qstats;
unsigned long state;
struct Qdisc *next_sched;
@@ -142,9 +143,13 @@ static inline struct Qdisc *qdisc_refcount_inc_nz(struct Qdisc *qdisc)
static inline bool qdisc_is_running(struct Qdisc *qdisc)
{
+#ifdef CONFIG_PREEMPT_RT_BASE
+ return spin_is_locked(&qdisc->running.lock) ? true : false;
+#else
if (qdisc->flags & TCQ_F_NOLOCK)
return spin_is_locked(&qdisc->seqlock);
return (raw_read_seqcount(&qdisc->running) & 1) ? true : false;
+#endif
}
static inline bool qdisc_is_percpu_stats(const struct Qdisc *q)
@@ -161,6 +166,11 @@ static inline bool qdisc_is_empty(const struct Qdisc *qdisc)
static inline bool qdisc_run_begin(struct Qdisc *qdisc)
{
+#ifdef CONFIG_PREEMPT_RT_BASE
+ if (try_write_seqlock(&qdisc->running))
+ return true;
+ return false;
+#else
if (qdisc->flags & TCQ_F_NOLOCK) {
if (spin_trylock(&qdisc->seqlock))
goto nolock_empty;
@@ -212,10 +222,14 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
raw_write_seqcount_begin(&qdisc->running);
seqcount_acquire(&qdisc->running.dep_map, 0, 1, _RET_IP_);
return true;
+#endif
}
static inline void qdisc_run_end(struct Qdisc *qdisc)
{
+#ifdef CONFIG_PREEMPT_RT_BASE
+ write_sequnlock(&qdisc->running);
+#else
if (qdisc->flags & TCQ_F_NOLOCK) {
spin_unlock(&qdisc->seqlock);
@@ -227,6 +241,7 @@ static inline void qdisc_run_end(struct Qdisc *qdisc)
} else {
write_seqcount_end(&qdisc->running);
}
+#endif
}
static inline bool qdisc_may_bulk(const struct Qdisc *qdisc)
@@ -544,7 +559,7 @@ static inline spinlock_t *qdisc_root_sleeping_lock(const struct Qdisc *qdisc)
return qdisc_lock(root);
}
-static inline seqcount_t *qdisc_root_sleeping_running(const struct Qdisc *qdisc)
+static inline net_seqlock_t *qdisc_root_sleeping_running(const struct Qdisc *qdisc)
{
struct Qdisc *root = qdisc_root_sleeping(qdisc);
diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
index 0969d93cb782..946190d7e1a3 100644
--- a/net/core/gen_estimator.c
+++ b/net/core/gen_estimator.c
@@ -46,7 +46,7 @@
struct net_rate_estimator {
struct gnet_stats_basic_packed *bstats;
spinlock_t *stats_lock;
- seqcount_t *running;
+ net_seqlock_t *running;
struct gnet_stats_basic_cpu __percpu *cpu_bstats;
u8 ewma_log;
u8 intvl_log; /* period : (250ms << intvl_log) */
@@ -129,7 +129,7 @@ int gen_new_estimator(struct gnet_stats_basic_packed *bstats,
struct gnet_stats_basic_cpu __percpu *cpu_bstats,
struct net_rate_estimator __rcu **rate_est,
spinlock_t *lock,
- seqcount_t *running,
+ net_seqlock_t *running,
struct nlattr *opt)
{
struct gnet_estimator *parm = nla_data(opt);
@@ -227,7 +227,7 @@ int gen_replace_estimator(struct gnet_stats_basic_packed *bstats,
struct gnet_stats_basic_cpu __percpu *cpu_bstats,
struct net_rate_estimator __rcu **rate_est,
spinlock_t *lock,
- seqcount_t *running, struct nlattr *opt)
+ net_seqlock_t *running, struct nlattr *opt)
{
return gen_new_estimator(bstats, cpu_bstats, rate_est,
lock, running, opt);
diff --git a/net/core/gen_stats.c b/net/core/gen_stats.c
index 9bf1b9ad1780..a5d587774653 100644
--- a/net/core/gen_stats.c
+++ b/net/core/gen_stats.c
@@ -142,7 +142,7 @@ __gnet_stats_copy_basic_cpu(struct gnet_stats_basic_packed *bstats,
}
void
-__gnet_stats_copy_basic(const seqcount_t *running,
+__gnet_stats_copy_basic(net_seqlock_t *running,
struct gnet_stats_basic_packed *bstats,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b)
@@ -155,15 +155,15 @@ __gnet_stats_copy_basic(const seqcount_t *running,
}
do {
if (running)
- seq = read_seqcount_begin(running);
+ seq = net_seq_begin(running);
bstats->bytes = b->bytes;
bstats->packets = b->packets;
- } while (running && read_seqcount_retry(running, seq));
+ } while (running && net_seq_retry(running, seq));
}
EXPORT_SYMBOL(__gnet_stats_copy_basic);
static int
-___gnet_stats_copy_basic(const seqcount_t *running,
+___gnet_stats_copy_basic(net_seqlock_t *running,
struct gnet_dump *d,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b,
@@ -204,7 +204,7 @@ ___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,
+gnet_stats_copy_basic(net_seqlock_t *running,
struct gnet_dump *d,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b)
@@ -228,7 +228,7 @@ 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,
+gnet_stats_copy_basic_hw(net_seqlock_t *running,
struct gnet_dump *d,
struct gnet_stats_basic_cpu __percpu *cpu,
struct gnet_stats_basic_packed *b)
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 844c11acce03..910670b8a5d7 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1201,7 +1201,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
rcu_assign_pointer(sch->stab, stab);
}
if (tca[TCA_RATE]) {
- seqcount_t *running;
+ net_seqlock_t *running;
err = -EOPNOTSUPP;
if (sch->flags & TCQ_F_MQROOT) {
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 5da52e4d3f56..85041afa9c4d 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -581,7 +581,11 @@ struct Qdisc noop_qdisc = {
.ops = &noop_qdisc_ops,
.q.lock = __SPIN_LOCK_UNLOCKED(noop_qdisc.q.lock),
.dev_queue = &noop_netdev_queue,
+#ifdef CONFIG_PREEMPT_RT_BASE
+ .running = __SEQLOCK_UNLOCKED(noop_qdisc.running),
+#else
.running = SEQCNT_ZERO(noop_qdisc.running),
+#endif
.busylock = __SPIN_LOCK_UNLOCKED(noop_qdisc.busylock),
.gso_skb = {
.next = (struct sk_buff *)&noop_qdisc.gso_skb,
@@ -918,9 +922,17 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
lockdep_set_class(&sch->busylock,
dev->qdisc_tx_busylock ?: &qdisc_tx_busylock);
+#ifdef CONFIG_PREEMPT_RT_BASE
+ seqlock_init(&sch->running);
+ lockdep_set_class(&sch->running.seqcount,
+ dev->qdisc_running_key ?: &qdisc_running_key);
+ lockdep_set_class(&sch->running.lock,
+ dev->qdisc_running_key ?: &qdisc_running_key);
+#else
seqcount_init(&sch->running);
lockdep_set_class(&sch->running,
dev->qdisc_running_key ?: &qdisc_running_key);
+#endif
sch->ops = ops;
sch->flags = ops->static_flags;
--
2.35.1