Add SPINLOCKS define in XioPortal.h, default to 1.

    Spinlocks appear to profile best.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Raise EPOLL timeout to 300.

Profiling suggests this value is effective for very high
message rates.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Disable dout(4) in XioMessenger hot path.

More profiling with different log levels may be adviseable here.  Profiling requires
minimal log traffic (i.e., none).

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Conditional xio_{client,server} DispatchStrategy.

Permits side-by-side profiling.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Inline buffer::list operations.

This has a massive impact on performance at high message rates.  Just moving
the operations into the buffer::list interface does the actual work.  I've added
the inline keyword as an annotation.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>