I applied this to master with the below incremental.
We _usually_ use positive error numbers in int return value.
I think there was an extra COVERAGE_INC(seq_change)
Thanks for the patch!
diff --git a/lib/ovs-rcu.c b/lib/ovs-rcu.c
index 7462579..8aef1f1 100644
--- a/lib/ovs-rcu.c
+++ b/lib/ovs-rcu.c
@@ -157,7 +157,7 @@ int
ovsrcu_try_quiesce(void)
{
struct ovsrcu_perthread *perthread;
- int ret = -EBUSY;
+ int ret = EBUSY;
ovs_assert(!single_threaded());
perthread = ovsrcu_perthread_get();
diff --git a/lib/seq.c b/lib/seq.c
index 4e99c6c..b8b5b65 100644
--- a/lib/seq.c
+++ b/lib/seq.c
@@ -138,8 +138,6 @@ void
seq_change(struct seq *seq)
OVS_EXCLUDED(seq_mutex)
{
- COVERAGE_INC(seq_change);
-
ovs_mutex_lock(&seq_mutex);
seq_change_protected(seq);
ovs_mutex_unlock(&seq_mutex);
2016-07-05 6:33 GMT-07:00 Flavio Leitner <f...@redhat.com>:
> The PMD thread needs to keep processing RX queues in order
> to achieve maximum throughput. It also needs to sweep emc
> cache and quiesce which use seq_mutex. That mutex can
> eventually block the PMD thread causing latency spikes and
> affecting the throughput.
>
> Since there is no requirement for running those tasks at a
> specific time, this patch extend seq API to allow tentative
> locking instead.
>
> Reported-by: Karl Rister <kris...@redhat.com>
> Co-authored-by: Karl Rister <kris...@redhat.com>
> Signed-off-by: Flavio Leitner <f...@redhat.com>
> ---
> lib/dpif-netdev.c | 5 +++--
> lib/ovs-rcu.c | 37 +++++++++++++++++++++++++++++++++++--
> lib/ovs-rcu.h | 1 +
> lib/seq.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++---
> lib/seq.h | 5 +++++
> 5 files changed, 90 insertions(+), 7 deletions(-)
>
> v4:
> - return EBUSY if lock is busy.
>
> v3:
> - addressed clang annotation feedbacks from Daniele
> - tested over 4 days without spikes or other issues
>
> v2:
> - expanded SEQ API instead of using recursive lock.
>
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 37c2631..dc5b02e 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -2869,9 +2869,10 @@ reload:
>
> lc = 0;
>
> - emc_cache_slow_sweep(&pmd->flow_cache);
> coverage_try_clear();
> - ovsrcu_quiesce();
> + if (!ovsrcu_try_quiesce()) {
> + emc_cache_slow_sweep(&pmd->flow_cache);
> + }
>
> atomic_read_relaxed(&pmd->change_seq, &seq);
> if (seq != port_seq) {
> diff --git a/lib/ovs-rcu.c b/lib/ovs-rcu.c
> index 0ff508e..7462579 100644
> --- a/lib/ovs-rcu.c
> +++ b/lib/ovs-rcu.c
> @@ -15,6 +15,7 @@
> */
>
> #include <config.h>
> +#include <errno.h>
> #include "ovs-rcu.h"
> #include "fatal-signal.h"
> #include "guarded-list.h"
> @@ -57,6 +58,7 @@ static struct guarded_list flushed_cbsets;
> static struct seq *flushed_cbsets_seq;
>
> static void ovsrcu_init_module(void);
> +static void ovsrcu_flush_cbset__(struct ovsrcu_perthread *, bool);
> static void ovsrcu_flush_cbset(struct ovsrcu_perthread *);
> static void ovsrcu_unregister__(struct ovsrcu_perthread *);
> static bool ovsrcu_call_postponed(void);
> @@ -151,6 +153,27 @@ ovsrcu_quiesce(void)
> ovsrcu_quiesced();
> }
>
> +int
> +ovsrcu_try_quiesce(void)
> +{
> + struct ovsrcu_perthread *perthread;
> + int ret = -EBUSY;
> +
> + ovs_assert(!single_threaded());
> + perthread = ovsrcu_perthread_get();
> + if (!seq_try_lock()) {
> + perthread->seqno = seq_read_protected(global_seqno);
> + if (perthread->cbset) {
> + ovsrcu_flush_cbset__(perthread, true);
> + }
> + seq_change_protected(global_seqno);
> + seq_unlock();
> + ovsrcu_quiesced();
> + ret = 0;
> + }
> + return ret;
> +}
> +
> bool
> ovsrcu_is_quiescent(void)
> {
> @@ -292,7 +315,7 @@ ovsrcu_postpone_thread(void *arg OVS_UNUSED)
> }
>
> static void
> -ovsrcu_flush_cbset(struct ovsrcu_perthread *perthread)
> +ovsrcu_flush_cbset__(struct ovsrcu_perthread *perthread, bool protected)
> {
> struct ovsrcu_cbset *cbset = perthread->cbset;
>
> @@ -300,11 +323,21 @@ ovsrcu_flush_cbset(struct ovsrcu_perthread
> *perthread)
> guarded_list_push_back(&flushed_cbsets, &cbset->list_node,
> SIZE_MAX);
> perthread->cbset = NULL;
>
> - seq_change(flushed_cbsets_seq);
> + if (protected) {
> + seq_change_protected(flushed_cbsets_seq);
> + } else {
> + seq_change(flushed_cbsets_seq);
> + }
> }
> }
>
> static void
> +ovsrcu_flush_cbset(struct ovsrcu_perthread *perthread)
> +{
> + ovsrcu_flush_cbset__(perthread, false);
> +}
> +
> +static void
> ovsrcu_unregister__(struct ovsrcu_perthread *perthread)
> {
> if (perthread->cbset) {
> diff --git a/lib/ovs-rcu.h b/lib/ovs-rcu.h
> index 8750ead..dc75749 100644
> --- a/lib/ovs-rcu.h
> +++ b/lib/ovs-rcu.h
> @@ -217,6 +217,7 @@ void ovsrcu_postpone__(void (*function)(void *aux),
> void *aux);
> void ovsrcu_quiesce_start(void);
> void ovsrcu_quiesce_end(void);
> void ovsrcu_quiesce(void);
> +int ovsrcu_try_quiesce(void);
> bool ovsrcu_is_quiescent(void);
>
> /* Synchronization. Waits for all non-quiescent threads to quiesce at
> least
> diff --git a/lib/seq.c b/lib/seq.c
> index 57e0775..4e99c6c 100644
> --- a/lib/seq.c
> +++ b/lib/seq.c
> @@ -100,6 +100,38 @@ seq_destroy(struct seq *seq)
> ovs_mutex_unlock(&seq_mutex);
> }
>
> +int
> +seq_try_lock(void)
> +{
> + return ovs_mutex_trylock(&seq_mutex);
> +}
> +
> +void
> +seq_lock(void)
> + OVS_ACQUIRES(seq_mutex)
> +{
> + ovs_mutex_lock(&seq_mutex);
> +}
> +
> +void
> +seq_unlock(void)
> + OVS_RELEASES(seq_mutex)
> +{
> + ovs_mutex_unlock(&seq_mutex);
> +}
> +
> +/* Increments 'seq''s sequence number, waking up any threads that are
> waiting
> + * on 'seq'. */
> +void
> +seq_change_protected(struct seq *seq)
> + OVS_REQUIRES(seq_mutex)
> +{
> + COVERAGE_INC(seq_change);
> +
> + seq->value = seq_next++;
> + seq_wake_waiters(seq);
> +}
> +
> /* Increments 'seq''s sequence number, waking up any threads that are
> waiting
> * on 'seq'. */
> void
> @@ -109,8 +141,7 @@ seq_change(struct seq *seq)
> COVERAGE_INC(seq_change);
>
> ovs_mutex_lock(&seq_mutex);
> - seq->value = seq_next++;
> - seq_wake_waiters(seq);
> + seq_change_protected(seq);
> ovs_mutex_unlock(&seq_mutex);
> }
>
> @@ -120,13 +151,25 @@ seq_change(struct seq *seq)
> * when an object changes, even without an ability to lock the object.
> See
> * Usage in seq.h for details. */
> uint64_t
> +seq_read_protected(const struct seq *seq)
> + OVS_REQUIRES(seq_mutex)
> +{
> + return seq->value;
> +}
> +
> +/* Returns 'seq''s current sequence number (which could change
> immediately).
> + *
> + * seq_read() and seq_wait() can be used together to yield a race-free
> wakeup
> + * when an object changes, even without an ability to lock the object.
> See
> + * Usage in seq.h for details. */
> +uint64_t
> seq_read(const struct seq *seq)
> OVS_EXCLUDED(seq_mutex)
> {
> uint64_t value;
>
> ovs_mutex_lock(&seq_mutex);
> - value = seq->value;
> + value = seq_read_protected(seq);
> ovs_mutex_unlock(&seq_mutex);
>
> return value;
> diff --git a/lib/seq.h b/lib/seq.h
> index f3f4b53..221ab9a 100644
> --- a/lib/seq.h
> +++ b/lib/seq.h
> @@ -121,9 +121,14 @@
> struct seq *seq_create(void);
> void seq_destroy(struct seq *);
> void seq_change(struct seq *);
> +void seq_change_protected(struct seq *);
> +void seq_lock(void);
> +int seq_try_lock(void);
> +void seq_unlock(void);
>
> /* For observers. */
> uint64_t seq_read(const struct seq *);
> +uint64_t seq_read_protected(const struct seq *);
>
> void seq_wait_at(const struct seq *, uint64_t value, const char *where);
> #define seq_wait(seq, value) seq_wait_at(seq, value, OVS_SOURCE_LOCATOR)
> --
> 2.5.5
>
>
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