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Replace the introduction to the SMPng page, which largely dated from 2003,

Browse source 
with a new introduction that reflects the work that has gone into the 5.x
and 6.x branches.  In particular, update the status to reflect MPSAFE
networking, MPSAFE VFS, MPSAFE VM, on-going performance work, and some of
the important steps to get there.  Highlight the iterative nature of the
work, and the focus on infrastructure.
This commit is contained in:
Robert Watson 2005-07-01 11:32:56 +00:00
parent fdba7ed1e3
commit 55d1820850
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/www/; revision=24994
1 changed files with 59 additions and 11 deletions
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70
en/smp/index.sgml
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@ -1,6 +1,6 @@
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" [
<!ENTITY base CDATA "..">
<!ENTITY date "$FreeBSD: www/en/smp/index.sgml,v 1.140 2005/01/23 20:47:25 keramida Exp $">
<!ENTITY date "$FreeBSD: www/en/smp/index.sgml,v 1.141 2005/04/05 20:47:58 jcamou Exp $">
<!ENTITY title "FreeBSD SMP Project">
<!ENTITY email 'freebsd-smp'>
<!ENTITY % includes SYSTEM "../includes.sgml"> %includes;
@ -37,16 +37,64 @@
<a name="goal"></a>
<h2>Project Goal</h2>
<p>The FreeBSD Symmetric MultiProcessing (SMP) project, often referred to as SMPng (SMP next
generation), is focused on implementing fine-grained SMP support
for the FreeBSD kernel. It debuted in 5.0-RELEASE in January of
2003. Due to FreeBSD's history, this is much like trying to fit
a square peg into a round hole, and as such, the intermediate
results aren't pretty in many ways. We are specifically not
attempting to rewrite the kernel from scratch, nor are we on a
crusade to fix all the architectural nits currently present in
the kernel. This is a pragmatic project rather than a
theoretical one.</p>
<p>The FreeBSD Symmetric MultiProcessing (SMP) project, often referred to
as SMPng (SMP next generation), is focused on introducing parallelism
into the FreeBSD kernel.
While earlier versions of FreeBSD (3.x, 4.x) supported parallelism in
user processes, the kernel was limited to executing on a single
processor at a time, using what is referred to as a "Giant lock" around
the kernel.
For many interesting workloads, this results in a substantial speed-up,
as significant computation occurs in user processes, especially for
applications such as rendering and compilation.
However, for kernel-intensive applications, such as intensive network
or file system I/O, contention on the kernel lock results in little
speed-up.
The end goal of the SMPng Project is to decompose the Giant lock into a
number of smaller locks, resulting in reduced contention (and improved
SMP performance).
However, important steps along the way include redesigning significant
portions of the FreeBSD kernel architecture around the notion of
ubiquitous parallelism: that at any moment, many processors might enter
the kernel at the same time.
This includes the introduction of more mature threading and
synchronization primitives, interrupt threads, cache-aware allocation
and scheduling, and topology-aware scheduling. </p>
<p>SMPng debuted in FreeBSD 5.0-RELEASE in January of 2005, and involved
over five years of continuous development by a large number of members
of the FreeBSD development team, as well as many external contributors.
Since 5.0, the implementation has substantially matured; in the 5.0
release, the basic architectural changes required to support SMPng were
complete, including new kernel memory allocators, synchronization
routines, the move to ithreads, and the removal of the Giant lock from
activities such as process scheduling and several common forms of IPC.
Since 5.0, the architecture has been refined in a number of ways,
including optimizing synchronization approaches, stability and
performance testing on larger systems (up to 12 processors), and the
removal of Giant from several significant parts of the operating
system, including large parts of Virtual Memory (VM), the Virtual File
System (VFS), UNIX File System (UFS), most parts of the network stack,
including IPv4, IPV6, FAST_IPSEC, UNIX domain sockets, and NetGraph,
and also from additional inter-process communication primitives.
The SMP-aware kernel slab allocator is now used almost universally, and
the focus has changed from "make it work", to "optimize it!".
The FreeBSD 5.3 kernel introduced Giant-free network stack execution
for most relevant code paths, and the FreeBSD 6.x kernel introduces
MPSAFE VFS, as well as wide-spread performance optimization.</p>
<p>Continuing work on SMPng includes work sweeping up the "loose ends"
that remain under Giant, such as parts of NFS, less widely used file
systems such as NTFS, and less commonly used network stack components,
such as SLIP.
Another important focus is performance measurement and optimization,
which build on and refine the SMPng architecture: the introduction of
features such as the kernel trace facility (KTR), hardware performance
monitor counters (hwpmc), lock profiling, and improved memory
monitoring play important roles in this process. Other important
debugging and testing facilities include WITNESS, a run-time kernel
lock order verifier, and wide-spread use of lock assertions and
run-time invariants testing.</p>
<a name="plan"></a>
<h2>Project Plan</h2>