pipe/fifo code merged.

[Giovanni Trematerra]

Hi,
the patch at
http://www.trematerra.net/patches/pipefifo_merge2.diff

is a preliminary version of the FIFO optimizations project that I picked up from
the wiki.
http://wiki.freebsd.org/IdeasPage#FIFO_optimizations_.28GSoC.29

zhaoshuai@ produced the following patch in the 2009 which attempted a first
merge of the interfaces:
http://www.trematerra.net/patches/fifo_soc2009.diff

However I felt like the work was not yet completed and come up with my final
version.
Now fifoes derive their structures from pipes one with just special handling
to support VFS operations.
All the operations but the creation/destruction for fifoes and pipes are handled
by the same code.
The heart of the patch is the new struct pipeinfo.
pipeinfo is a per-file descriptor state. Basically it maintains a read end and
a write end for the descriptor. As pipes are bidirectional in FreeBSD, for a
pipe this two fields are always equal but different for a fifo.
To let fifo code in sys/fs/fifofs/fifo_vnops.c create/destroy the pipe, two
functions (pipe_ctor/pipe_dtor) were written. pipe_ctor setups things like a
call to kern_pipe and return a pipeinfo structure, while pipe_dtor releases
all the resources for a given pipeinfo. Once a pipe was setup during a fifo_open
call, all the subsequent operations on the fifo are handled by the same code
of a pipe expect for the clean up code that calls pipe_dtor.
Allocation of two pipeinfo structures for a pipe were showed to slow down
things by some micro-benchmarking. To speed up things during
creation/destruction of pipes, the patch allocates all the needed data structure
zone using the umapipe struct that packing together all the needed data
structures to be allocated at pipe creation. A similar umafifo structure is
used for fifoes.
Thanks to jilles that made a review of the patch in a previous form, privately.
Thanks a lot to attilio that answered my stupid questions and drove me in the
right direction.

TEST
The patch passed all the test in tools/regression/pipe and tools/regression/fifo
it passed a overnight of running stress test pho's suite and some
buildworld/buildkernel of FreeBSD HEAD.

PERFORMANCE
the patch doesn't add any performance penalty at pipe code, the test was
performed by compiling a GENERIC kernel. There's a lot of pipe code involving
during a compilation. Such a test was used to discovery a performance
regression in r226042.

this is the ministat output
http://www.trematerra.net/patches/pipeperf/pipeperf_result

here the raw data
http://www.trematerra.net/patches/pipeperf/pipeperf_rawresult

The new fifo implementation gives to fifoes a boost of at least 15% in avarage.
The test was send 1000 chunk of different size through a fifo.

here the output of ministat output
http://www.trematerra.net/patches/fifoperf/fifoperf_result

here the raw results
http://www.trematerra.net/patches/fifoperf/fifoperf_rawresult

if someone would like to reproduce the test can download a copy of the sources a
http://www.trematerra.net/patches/fifoperf/

the code is from zhaoshuai at .
Makefile,
builds benchmark.c

benchmark.c
set up a fifo, fork and send a number of messages of a size depending from
the input parameters.

runme.sh
run the test launching benchmark binary to send different number of messages of
different sizes.

Test and review are welcomed.

--
Gianni