Resource temporarily unavailable 超高并发如何优化内核

小流量超高并发环境，系统持续报 Resource temporarily unavailable，当前内核 ulimit 情况如下：

core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 515066
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1000000
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 1000000
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

cpu 占用 10%，内存占用情况如下：
total used free shared buffers cached
Mem: 2000 1797 202 0 1 92
-/+ buffers/cache: 1704 295
Swap: 3999 760 3239

请问还有哪些可以进一步优化的地方，请不吝赐教。谢谢！