ipvs: wakeup master thread

	High rate of sync messages in master can lead to
overflowing the socket buffer and dropping the messages.
Fixed sleep of 1 second without wakeup events is not suitable
for loaded masters,

	Use delayed_work to schedule sending for queued messages
and limit the delay to IPVS_SYNC_SEND_DELAY (20ms). This will
reduce the rate of wakeups but to avoid sending long bursts we
wakeup the master thread after IPVS_SYNC_WAKEUP_RATE (8) messages.

	Add hard limit for the queued messages before sending
by using "sync_qlen_max" sysctl var. It defaults to 1/32 of
the memory pages but actually represents number of messages.
It will protect us from allocating large parts of memory
when the sending rate is lower than the queuing rate.

	As suggested by Pablo, add new sysctl var
"sync_sock_size" to configure the SNDBUF (master) or
RCVBUF (slave) socket limit. Default value is 0 (preserve
system defaults).

	Change the master thread to detect and block on
SNDBUF overflow, so that we do not drop messages when
the socket limit is low but the sync_qlen_max limit is
not reached. On ENOBUFS or other errors just drop the
messages.

	Change master thread to enter TASK_INTERRUPTIBLE
state early, so that we do not miss wakeups due to messages or
kthread_should_stop event.

Thanks to Pablo Neira Ayuso for his valuable feedback!

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 29 insertions, 0 deletions

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 93b81aa73429..30e43c8c0283 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -869,6 +869,8 @@ struct netns_ipvs {
 #endif
         int                     sysctl_snat_reroute;
         int                     sysctl_sync_ver;
+        int                     sysctl_sync_qlen_max;
+        int                     sysctl_sync_sock_size;
         int                     sysctl_cache_bypass;
         int                     sysctl_expire_nodest_conn;
         int                     sysctl_expire_quiescent_template;
@@ -889,6 +891,9 @@ struct netns_ipvs {
         struct timer_list       est_timer;      /* Estimation timer */
         /* ip_vs_sync */
         struct list_head        sync_queue;
+        int                     sync_queue_len;
+        unsigned int            sync_queue_delay;
+        struct delayed_work     master_wakeup_work;
         spinlock_t              sync_lock;
         struct ip_vs_sync_buff  *sync_buff;
         spinlock_t              sync_buff_lock;
@@ -911,6 +916,10 @@ struct netns_ipvs {
 #define DEFAULT_SYNC_THRESHOLD  3
 #define DEFAULT_SYNC_PERIOD     50
 #define DEFAULT_SYNC_VER        1
+#define IPVS_SYNC_WAKEUP_RATE   8
+#define IPVS_SYNC_QLEN_MAX      (IPVS_SYNC_WAKEUP_RATE * 4)
+#define IPVS_SYNC_SEND_DELAY    (HZ / 50)
+#define IPVS_SYNC_CHECK_PERIOD  HZ
 
 #ifdef CONFIG_SYSCTL
 
@@ -929,6 +938,16 @@ static inline int sysctl_sync_ver(struct netns_ipvs *ipvs)
         return ipvs->sysctl_sync_ver;
 }
 
+static inline int sysctl_sync_qlen_max(struct netns_ipvs *ipvs)
+{
+        return ipvs->sysctl_sync_qlen_max;
+}
+
+static inline int sysctl_sync_sock_size(struct netns_ipvs *ipvs)
+{
+        return ipvs->sysctl_sync_sock_size;
+}
+
 #else
 
 static inline int sysctl_sync_threshold(struct netns_ipvs *ipvs)
@@ -946,6 +965,16 @@ static inline int sysctl_sync_ver(struct netns_ipvs *ipvs)
         return DEFAULT_SYNC_VER;
 }
 
+static inline int sysctl_sync_qlen_max(struct netns_ipvs *ipvs)
+{
+        return IPVS_SYNC_QLEN_MAX;
+}
+
+static inline int sysctl_sync_sock_size(struct netns_ipvs *ipvs)
+{
+        return 0;
+}
+
 #endif
 
 /*