[PATCH v2 net-next 0/1] net: lls select poll support

[Eliezer Tamir <eliezer.tamir@linux.intel.com>]

David,

Here is a rework of the select/poll patch.
(I called this a v2 but we are continuing where we left off in v9
of the original series.)

One question: do we need in sock_poll() to test that sock->sk is not null?
(Thanks to Willem de Bruijn for pointing this out.) 

When select or poll are used on a lot of sockets the sysctl value
needs to be set higher than 50. For 300 sockets a setting of 100 works
for me. For 1000 sockets a setting of 200 works well but the gain is
very small, probably not worth it.

I should mention that unlike the version we had in v9, with this version
of the patch, LLS always performs better than no LLS. 

-Eliezer

Change log:
v2
- added POLL_LL flag, used to signal between the syscalls and sock_poll().
- add a separate ll_end_time() function to be used from poll.
- slight reorder of sk_poll_ll so the timing primitives are not used
  when called from sock_poll().
- select/poll stop busy polling as soon as there is something to return
  to the user.

Change log from the original LLS patch series:
v9
- better mask testing in sock_poll(), reported by Eric Dumazet.

v8
- split out udp and select/poll into separate patches.
  what used to be patch 2/5 is now three patches.

v5
- added simple poll/select support