net: poll/select low latency socket support
select/poll busy-poll support.
Split sysctl value into two separate ones, one for read and one for poll.
updated Documentation/sysctl/net.txt
Add a new poll flag POLL_LL. When this flag is set, sock_poll will call
sk_poll_ll if possible. sock_poll sets this flag in its return value
to indicate to select/poll when a socket that can busy poll is found.
When poll/select have nothing to report, call the low-level
sock_poll again until we are out of time or we find something.
Once the system call finds something, it stops setting POLL_LL, so it can
return the result to the user ASAP.
Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ll_poll.h b/include/net/ll_poll.h
index fcc7c36..5bf2b3a 100644
--- a/include/net/ll_poll.h
+++ b/include/net/ll_poll.h
@@ -30,6 +30,7 @@
#ifdef CONFIG_NET_LL_RX_POLL
struct napi_struct;
+extern unsigned int sysctl_net_ll_read __read_mostly;
extern unsigned int sysctl_net_ll_poll __read_mostly;
/* return values from ndo_ll_poll */
@@ -38,17 +39,18 @@
/* we can use sched_clock() because we don't care much about precision
* we only care that the average is bounded
+ * we don't mind a ~2.5% imprecision so <<10 instead of *1000
+ * sk->sk_ll_usec is a u_int so this can't overflow
*/
-static inline u64 ll_end_time(struct sock *sk)
+static inline u64 ll_sk_end_time(struct sock *sk)
{
- u64 end_time = ACCESS_ONCE(sk->sk_ll_usec);
+ return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + sched_clock();
+}
- /* we don't mind a ~2.5% imprecision
- * sk->sk_ll_usec is a u_int so this can't overflow
- */
- end_time = (end_time << 10) + sched_clock();
-
- return end_time;
+/* in poll/select we use the global sysctl_net_ll_poll value */
+static inline u64 ll_end_time(void)
+{
+ return ((u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10) + sched_clock();
}
static inline bool sk_valid_ll(struct sock *sk)
@@ -62,10 +64,13 @@
return !time_after64(sched_clock(), end_time);
}
+/* when used in sock_poll() nonblock is known at compile time to be true
+ * so the loop and end_time will be optimized out
+ */
static inline bool sk_poll_ll(struct sock *sk, int nonblock)
{
+ u64 end_time = nonblock ? 0 : ll_sk_end_time(sk);
const struct net_device_ops *ops;
- u64 end_time = ll_end_time(sk);
struct napi_struct *napi;
int rc = false;
@@ -84,7 +89,6 @@
goto out;
do {
-
rc = ops->ndo_ll_poll(napi);
if (rc == LL_FLUSH_FAILED)
@@ -95,8 +99,8 @@
NET_ADD_STATS_BH(sock_net(sk),
LINUX_MIB_LOWLATENCYRXPACKETS, rc);
- } while (skb_queue_empty(&sk->sk_receive_queue)
- && can_poll_ll(end_time) && !nonblock);
+ } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
+ can_poll_ll(end_time));
rc = !skb_queue_empty(&sk->sk_receive_queue);
out:
@@ -118,7 +122,12 @@
#else /* CONFIG_NET_LL_RX_POLL */
-static inline u64 ll_end_time(struct sock *sk)
+static inline u64 sk_ll_end_time(struct sock *sk)
+{
+ return 0;
+}
+
+static inline u64 ll_end_time(void)
{
return 0;
}