net: rename low latency sockets functions to busy poll

Rename functions in include/net/ll_poll.h to busy wait.
Clarify documentation about expected power use increase.
Rename POLL_LL to POLL_BUSY_LOOP.
Add need_resched() testing to poll/select busy loops.

Note, that in select and poll can_busy_poll is dynamic and is
updated continuously to reflect the existence of supported
sockets with valid queue information.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/sysctl/net.txt

@@ -53,22 +53,24 @@ Default: 64
 low_latency_read
 ----------------
 Low latency busy poll timeout for socket reads. (needs CONFIG_NET_LL_RX_POLL)
-Approximate time in us to spin waiting for packets on the device queue.
+Approximate time in us to busy loop waiting for packets on the device queue.
 This sets the default value of the SO_LL socket option.
-Can be set or overridden per socket by setting socket option SO_LL.
-Recommended value is 50. May increase power usage.
+Can be set or overridden per socket by setting socket option SO_LL, which is
+the preferred method of enabling.
+If you need to enable the feature globally via sysctl, a value of 50 is recommended.
+Will increase power usage.
 Default: 0 (off)
 
 low_latency_poll
 ----------------
 Low latency busy poll timeout for poll and select. (needs CONFIG_NET_LL_RX_POLL)
-Approximate time in us to spin waiting for packets on the device queue.
+Approximate time in us to busy loop waiting for events.
 Recommended value depends on the number of sockets you poll on.
 For several sockets 50, for several hundreds 100.
 For more than that you probably want to use epoll.
 Note that only sockets with SO_LL set will be busy polled, so you want to either
 selectively set SO_LL on those sockets or set sysctl.net.low_latency_read globally.
-May increase power usage.
+Will increase power usage.
 Default: 0 (off)
 
 rmem_default