Import Alan Cox's /usr/src/sys/kern/sys_pipe.c 1.171. This rips out

Import Alan Cox's /usr/src/sys/kern/sys_pipe.c 1.171.  This rips out
writer-side KVA mappings and replaces them with writer-side vm_page wiring
(left intact from before) plus reader-side SF_BUF copies.

Import 1.141, which is a simple patch which removes a blocking condition
when space is available in the pipe's write buffer which was causing
non-blocking I/O select-based writes to spin-wait unnecessarily.  1.171
rips out writer-side KVA mappings and replaces them

Import FreeBSD-5.x's uiomove_fromphys(), which sys_pipe.c now uses.  This
procedure could become very useful in a number of DragonFly subsystems.

This greatly improves PIPE performance for the direct-mapped case (moderate
to large reads and writes).  Additionally, recent scheduler fixes greatly
improve PIPE performance for both the direct-mapped and small-buffer cases.

NOTE: wired page limits for pipes have not yet been imported, and the heavy
use of sf_buf's may require some tuning in the many-pipes case.

    BLKSIZE	BEFORE		AFTER
		MBytes/s	MBytes/s	Tests on AMD64/3200+ FN85 MB
    -------	------		------		(64KB L1, 1MB L2)
    256KB	1900		2200
     64KB	1800		2200
     16KB	1650		2500-3000
      8KB	1400		2300
      4KB	1300		1400-1500	(note 1)

    note 1: The 4KB case is not a direct-write case, the results are due to
    the scheduler fixes only.

Obtained-from: FreeBSD-5.x / FreeBSD's Alan Cox