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>

2 files changed, 9 insertions, 1 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index 1e744b12fda3..b6c619f4d47b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2307,7 +2307,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 #ifdef CONFIG_NET_LL_RX_POLL
         sk->sk_napi_id          =       0;
-        sk->sk_ll_usec          =       sysctl_net_ll_poll;
+        sk->sk_ll_usec          =       sysctl_net_ll_read;
 #endif
 
         /*
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 62702c2053de..afc677eadd93 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -306,6 +306,14 @@ static struct ctl_table net_core_table[] = {
                 .mode           = 0644,
                 .proc_handler   = proc_dointvec
         },
+        {
+                .procname       = "low_latency_read",
+                .data           = &sysctl_net_ll_read,
+                .maxlen         = sizeof(unsigned int),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec
+        },
+#
 #endif
 #endif /* CONFIG_NET */
         {