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<!DOCTYPE article PUBLIC "-//FreeBSD//DTD DocBook V4.1-Based Extension//EN" [
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<!ENTITY t.releng.3 "<literal>RELENG_3</literal>">
<!ENTITY t.releng.4 "<literal>RELENG_4</literal>">
<!ENTITY t.releng.5 "<literal>RELENG_5</literal>">
<!ENTITY t.releng.5.1 "<literal>RELENG_5_1</literal>">
<!ENTITY t.releng.5.2 "<literal>RELENG_5_2</literal>">
<!ENTITY t.releng.head "<literal>HEAD</literal>">
]>
<article>
<articleinfo>
<title>The Roadmap for 5-STABLE</title>
<authorgroup>
<corpauthor>The &os; Release Engineering Team</corpauthor>
</authorgroup>
<pubdate>$FreeBSD$</pubdate>
<copyright>
<year>2003</year>
<holder role="mailto:re@FreeBSD.org">The &os; Release
Engineering Team</holder>
</copyright>
<legalnotice id="trademarks" role="trademarks">
&tm-attrib.freebsd;
&tm-attrib.ieee;
&tm-attrib.intel;
&tm-attrib.sparc;
&tm-attrib.sun;
&tm-attrib.opengroup;
&tm-attrib.general;
</legalnotice>
</articleinfo>
<sect1 id="intro">
<title>Introduction and Background</title>
<para>After nearly three years of work, &os; 5.0 was released in January
of 2003. Features like the GEOM block layer, Mandatory Access Controls,
ACPI, &sparc64; and ia64 platform support, and UFS snapshots, background
filesystem checks, and 64-bit inode sizes make it an exciting operating
system for both desktop and production users. However, some important
features are not complete. The foundations for fine-grained locking
and preemption in the kernel exist, but much more work is left to be
done. Work on Kernel Schedulable Entities (KSE), similar to Scheduler
Activations, has been ongoing but needs a push to realize its benefit.
Performance compared to &os; 4.<replaceable>X</replaceable> has
declined and must be restored and surpassed.</para>
<para>This is somewhat similar to the situation that &os; faced in the
3.<replaceable>X</replaceable> series. Work on 3-CURRENT trudged along
seemingly forever, and finally a cry was made to <quote>just ship it</quote> and
clean up later. This decision resulted in the 3.0 and 3.1 releases
being very unsatisfying for most, and it wasn't until 3.2 that the
series was considered <quote>stable</quote>. To make matters worse, the &t.releng.3;
branch was created along with the 3.0 release, and the &t.releng.head; branch was
allowed to advance immediately towards 4-CURRENT. This resulted in a
quick divergence between &t.releng.head; and &t.releng.3;, making maintenance of the
&t.releng.3; branch very difficult. &os; 2.2.8 was left for quite a while
as the last production-quality version of &os;.</para>
<para>Our intent is to avoid repeating that scenario with &os; 5.x.
Delaying the &t.releng.5; branch until it is stable and production quality
will ensure that it stays maintainable and provides a compelling reason
to upgrade from 4.<replaceable>X</replaceable>, To do this, we must
identify the current areas of weakness and set clear goals for
resolving them. This document contains what we as the release
engineering team feel are the milestones and issues that must be
resolved for the &t.releng.5; branch. It does not dictate every aspect of
&os; development, and we welcome further input. Nothing that follows
is meant to be a sleight against any person or group, or to trivialize
any work that has been done. There are some significant issues,
though, that need decisive and unbiased action.</para>
</sect1>
<sect1 id="major-issues">
<title>Major issues</title>
<para>The state of SMPng and kernel lockdown is the biggest concern for
5.<replaceable>X</replaceable>. To date, few major systems have come
out from under the kernel-wide mutex known as <quote>Giant</quote>.
The SMP status page at <ulink url="http://www.FreeBSD.org/smp"></ulink>
provides a comprehensive breakdown
of the overall SMPng status. Status specific to SMPng progress in
device drivers can be found at at
<ulink url="http://www.FreeBSD.org/projects/busdma"></ulink>.
In summary:</para>
<itemizedlist>
<listitem>
<para>VM: the kmem_malloc(M_NOWAIT) path no longer needs Giant held.
The kmem_malloc(M_WAITOK) path is in progress and is expected to be
finished in the coming weeks. Other facets of the VM system, like
the VFS interface, buffer/cache, etc, are largely untouched.</para>
</listitem>
<listitem>
<para>GEOM: The GEOM block layer was designed to run free of Giant,
but at this time no block drivers can run without Giant.
Additionally, it has the potential to suffer performance loss due
to its upcall/downcall data paths happening in kernel threads.
Lightweight context switches might help this.</para>
</listitem>
<listitem>
<para>Network: Locking of the TCP and UDP portions of the stack is
complete. Work is in progress to lock up the IP stack, including
the routing tree, ARP code, raw IP, and ifaddr and inet data
structures. IPv6 has been lightly touched during the inp locking
but is hindered by the KAME code being significantly out of date.
Work has not started on any of the other protocols such as
AppleTalk, XNS, or IPX. Locking of the socket layer is in progress
but has been largely untested. None of the hardware drivers or
Ethernet layers have been locked.</para>
</listitem>
<listitem>
<para>VFS: Initial pre-cleanup started.</para>
</listitem>
<listitem>
<para>buffer/cache: Initial work complete.</para>
</listitem>
<listitem>
<para>Proc: Work on locking the proc structure was ongoing for a
while but seems to have stalled.</para>
</listitem>
<listitem>
<para>CAM: No significant work has occurred on the CAM SCSI
layer.</para>
</listitem>
<listitem>
<para>Newbus: some work has started on locking down the device_t
structure.</para>
</listitem>
<listitem>
<para>Pipes: complete with the exception of VM-related
optimizations.</para>
</listitem>
<listitem>
<para>File descriptors: complete.</para>
</listitem>
<listitem>
<para>Process accounting: jails, credentials, MAC labels, and
scheduler are out from under Giant.</para>
</listitem>
<listitem>
<para>MAC Framework: complete</para>
</listitem>
<listitem>
<para>Timekeeping: complete</para>
</listitem>
<listitem>
<para>kernel encryption: crypto drivers and core &man.crypto.4; framework are
Giant-free. KAME IPsec and FAST IPSec have not been locked.</para>
</listitem>
<listitem>
<para>Sound subsystem: complete</para>
</listitem>
<listitem>
<para>kernel preemption: preemption for interrupt threads is enabled.
However, contention due to Giant covering much of the kernel and
most of the device driver interrupt routines causes excessive
context switches and might actually be hurting performance. Work
is underway to explore ways to make preemption be
conditional.</para>
</listitem>
</itemizedlist>
<para>Another issue with SMPng is interrupt latency. The overhead of
doing a complete context switch to a kernel interrupt thread is high
and shows noticeable latency. Work is ongoing to implement lazy
context switching on all platforms. Fine grained locking of drivers
will also help this, as will converting drivers to be as efficient as
possible in their interrupt routines.</para>
<para>Next, the state of KSE must resolved for &t.releng.5;. Work on it has
slowed noticeably in the past 6 months but appears to be picking up
again. There are a number of issues that must be addressed:</para>
<itemizedlist>
<listitem>
<para>The userland threading library, currently called libkse, is
immature and has not been used for any significant threaded
application.</para>
</listitem>
<listitem>
<para>KSE has the potential to uncover latent race conditions and
create new ones. An audit needs to be performed to ensure that no
obvious problems exist.</para>
</listitem>
</itemizedlist>
<para>According to the release schedule below, KSE kernel and userland
components must be functionality complete by June 2003 in order to be
included in the &t.releng.5; branch. For security and stability reasons,
if KSE cannot be finished in time then, by default, all KSE-specific
syscalls should be modified to return ENOSYS and all other KSE-specific
interfaces disabled. Deprecating KSE from &t.releng.5; but keeping it in
the &t.releng.head; branch will pose problems in porting bugfixes and features
between the two branches, so every effort should be made to finish it
on time.</para>
</sect1>
<sect1 id="goals">
<title>Goals for 5-STABLE</title>
<para>The goals for the &t.releng.5; branch point are:</para>
<itemizedlist>
<listitem>
<para>All subsystems and interfaces must be mature enough to be
maintainable for improvements and bug fixes.</para>
</listitem>
<listitem>
<para>Equal or better stability from &os; 4.8.</para>
</listitem>
<listitem>
<para>No functional regressions from 4.8. It is important to make
sure that users do not avoid upgrading to 5.x because of lost
functionality.</para>
</listitem>
<listitem>
<para>Performance on par with &os; 4.8 for most common operations.
Both UP and SMP configurations should be evaluated. SMP has the
potential to perform much better than
4.<replaceable>X</replaceable>, though for the purposes of creating
the &t.releng.5; branch, comparable performance between the two should
be acceptable.</para>
</listitem>
</itemizedlist>
<para>It is unrealistic to expect that the SMPng project will be fully
complete by &t.releng.5;, or that performance will be significantly better
than 4.<replaceable>X</replaceable>. However, focusing on a subset of
the outstanding tasks will give enough benefit for the branch to be
viable and maintainable. To break it down:</para>
<itemizedlist>
<listitem>
<para>ABI/API/Infrastructure stability - Enough infrastructure must
be in place and stable to allow fixes from &t.releng.head; to easily and
safely be merged into &t.releng.5;. Also, we must draw a line as to
what subsystems are to be locked down when we go into
5-STABLE.</para>
<itemizedlist>
<listitem>
<para>SMPng</para>
<itemizedlist>
<listitem>
<para>VM: Most codepaths, others than the ones that interact with
VFS, should be Giant-free for &t.releng.5;.</para>
</listitem>
<listitem>
<para>Network: Taking the network stack out from under Giant poses
the risk of uncovering latent bugs and races. Locking it down
but not removing Giant imposes further performance penalties. A
decision on which parts of the network stack should be locked and
taken out from under Giant for &t.releng.5; should be made no later
than March 15. Work on the IP, TCP, UDP,raw IP, routing sockets,
and &unix; domain sockets stands a good chance of being complete in
time for &t.releng.5;.</para>
<para>If the decision is made to not lift Giant from the stack,
then the locks in these layers could be optimized out with a
kernel config option. Having a Giant-free path from the the
hardware layer to the IP queues should be investigated as it
could allow significant performance gains in the network
benchmarks. If this can be achieved then the hardware interface
layer needs to allow for drivers to incrementally become free of
Giant. Locking down at least two Ethernet drivers would be
highly desirable. If the semantics are too complex to have the
stack free of Giant but not the hardware drivers, investigation
should be done into making it configurable.</para>
<para>Lesser-used network stacks like netatalk, netipx, etc, should
not break while this work is going on. However, locking them is
not a high priority. Special kernel config options might be
needed in order for these layers to operate with the rest of the
stack being locked and Giant free.</para>
</listitem>
<listitem>
<para>GEOM: At least 2 block drivers should be locked in order to
demonstrate that others can also be locked without changing the
interface to GEOM. The ATA driver is a good candidate for this,
though caution should be taken as it is also extremely
high-profile and any problems with it will affect nearly all
users of &os;.</para>
</listitem>
<listitem>
<para>Lazy context switching: sparc64 is the only platform that
performs lazy context switching when entering the kernel. The
performance gains promised by this are significant enough to
require that it be implemented for all other Tier-1
platforms.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>KSE: The kernel side of KSE must be functionally complete and
have undergone a security audit. libkse must be complete enough to
demonstrate a real-world application running correctly on it using
the standard &posix; Threads API. Examples would be apache 2.0,
&java;, and/or mozilla. A functional regression test suite is also a
requirement for &t.releng.5; and should test signal delivery,
scheduling, performance, and process security/credentials for both
KSE and non-KSE processes. KSE kernel and userland components must
also reach the same level of functionality for all Tier-1 platforms
in both UP and SMP configurations. The definition of <quote>Tier-1
platforms</quote> can be found in
<ulink url="http://www.FreeBSD.org/doc/en_US.ISO8859-1/articles/committers-guide/archs.html"></ulink>.</para>
</listitem>
<listitem>
<para>busdma interface and drivers: architectures like PAE/&i386; and
sparc64 which don't have a direct mapping between host memory
address space and expansion bus address space require the
elimination for vtophys() and friends. The busdma interface was
created to handle exactly this problem, but many drivers do not use
it yet. The busdma project at
<ulink url="http://www.FreeBSD.org/projects/busdma"></ulink>
tracks the
progress of this and should be used to determine which drivers
must be converted for &t.releng.5; and which can be left behind.
Also, there has been talk by several developers and the original
author to give the busdma interface a minor overhaul. If this is
to happen, it needs to happen before &t.releng.5;. Otherwise,
differences between the old and new API will make driver
maintenance difficult.</para>
</listitem>
<listitem>
<para>PCI resource allocation: PC2003 compliance requires that x86
systems no longer configure PCI devices from the system BIOS,
leaving this task solely to the OS. &os; must gain the ability to
manage and allocate PCI memory resources on its own. Implementing
this should take into account cardbus, PCI-HotPlug, and laptop
dockstation requirements. This feature will become increasingly
critical through the lifetime of &t.releng.5;, and therefore is a
requirement for the &t.releng.5; branch.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>Performance: most performance gains hinge on the progress of
SMPng Areas that should be concentrated on are:</para>
<itemizedlist>
<listitem>
<para>Storage I/O: I/O performance suffers from two problems, too
many expensive context switches, and too much work being done
in interrupt threads. Specifically, it takes 3 context
switches for most drivers to get from the hardware completion
interrupt to unblocking the user process: one for the
interrupt thread, one for the GEOM g_up thread, and one to get
back to the user thread. Drivers that attempt to be efficient
and quick in their interrupt handlers (as all should be)
usually also schedule a taskqueue, which adds a context switch
in between the interrupt thread and the g_up thread and brings
the total up to 4. Two things need to be done to attack
this:</para>
<itemizedlist>
<listitem>
<para>Make all drivers defer most of their processing out of
their interrupt thread. Significant performance gains have
been shown recently in the &man.aac.4; driver by making its
interrupt handler be <literal>INTR_MPSAFE</literal> and moving
all processing to a taskqueue.</para>
</listitem>
<listitem>
<para>investigate eliminating the taskqueue context switch by
adding a callback to the g_up thread that allows a driver to
do its interrupt processing there instead of in the
taskqueue.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>Network: Network drivers suffer from the interrupt latency
previously mentioned as well as from the network stack being
partially locked down but not free from Giant. Possible
strategies for addressing this are described in the previous
section.</para>
</listitem>
<listitem>
<para>Other locking - XXX?</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>Benchmarks and performance testing: Having a source of reliable
and useful benchmarks is essential to identifying performance
problems and guarding against performance regressions. A
<quote>performance team</quote> that is made up of people and
resources for formulating, developing, and executing benchmark
tests should be put into place soon. Comparisons should be made
against both &os; 4.<replaceable>X</replaceable> and Linux 2.4.x.
Tests to consider are:</para>
<itemizedlist>
<listitem>
<para>the classic <quote>worldstone</quote></para>
</listitem>
<listitem>
<para>webstone: <filename role="package">www/webstone</filename></para>
</listitem>
<listitem>
<para>Fstress: <ulink url="http://www.cs.duke.edu/ari/fstress"></ulink></para>
</listitem>
<listitem>
<para>ApacheBench: <filename role="package">www/p5-ApacheBench</filename></para>
</listitem>
<listitem>
<para>netperf: <filename role="package">benchmarks/netperf</filename></para>
</listitem>
<listitem>
<para>Web Polygraph: <ulink url="http://www.web-polygraph.org"></ulink>
Note: does not compile with gcc 3.x yet.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>Features:</para>
<itemizedlist>
<listitem>
<para>ACPI: Intel's ACPI power management and device configuration
subsystem has become an integral part of &os;'s x86 and ia64
device configuration model. However, many bugs exist in Intel's
vendor code, our OS-specific code, and motherboard BIOSes, causing
many ACPI-enabled systems to fail to boot, misdetect drivers,
and/or have many other problems. Fixing these problems seems to
be an uphill battle and is often times causing a poor
first-impression of &os; 5.0. Most x86 systems can function with
ACPI disabled, and logic should be added to the boot loader and
sysinstall to allow users to easily and intuitively turn it off.
Turning off ACPI by default is prone to problems also as many
newer systems rely on it to provide correct interrupt routing
information. Also, a centralized resource should be created to
track ACPI problems and solutions. Linux uses the same Intel
vendor sources as &os;, so we should investigate how they have
handled some of the known problems.</para>
</listitem>
<listitem>
<para>NEWCARD/OLDCARD: The NEWCARD subsystem was made the default
for &os; 5.0. Unfortunately, it contains no support for
non-Cardbus bridges and falls victim to interrupt routine
problems on some laptops. The classic 16-bit bridge support,
OLDCARD, still exists and can be compiled in, but this is highly
inconvenient for users of older laptops. If OLDCARD cannot be
completely deprecated for &t.releng.5;, then provisions must be made
to allow users to easily install an OLDCARD-enabled kernel.
Documentation should be written to help transition users from
OLDCARD to NEWCARD and from &man.pccardd.8; to
&man.devd.8;. The power management and
<quote>dumpcis</quote> functionality of &man.pccardc.8; needs to be
brought forward to work with NEWCARD, along with the ability to
load CIS quirk entries. Most of this functionality can be
integrated into &man.devd.8; and
&man.devctl.4;.</para>
</listitem>
<listitem>
<para>New scheduler framework: The new scheduler framework is in
place, and users can select between the classic 44bsd scheduler
and the new ULE scheduler. A scheduler that demonstrates
processor affinity, HyperThreading and KSE awareness, and no
regressions in performance or interactivity characteristics must
be available for &t.releng.5;.</para>
</listitem>
<listitem>
<para>sparc64 local console: neither syscons nor vt work on
sparc64, leaving it with only serial and <quote>fake</quote> OFW
console support. This is a major support hole for what is a
Tier-1 platform. Whether syscons can be shoe-horned in or
wscons be adopted from NetBSD is up for debate. However,
sparc64 must have local console support for &t.releng.5;. Having
this will also enable the XFree86 server to run, which is also a
requirement for &t.releng.5;.</para>
</listitem>
<listitem>
<para>gcc/toolchain: gcc 3.3 might be available in time for
&t.releng.5; and might offer some attractive benefits, but also
likely to introduce ABI incompatibility with prior gcc versions.
ABI compatibility should be locked down for the &t.releng.5;
branch.</para>
<para>There has also been a request to move /usr/include/g++ to
/usr/include/g++-v3 to be more compliant with the stock behavior
of gcc. This should also be investigated for &t.releng.5;.</para>
</listitem>
<listitem>
<para>gdb: gdb from the base system should work for sparc64. It
should also understand KSE thread semantics, assuming that KSE
is included in the &t.releng.5; branch. gdb 5.3 is available and
there are reports that it should address the sparc64 issue.</para>
</listitem>
<listitem>
<para>&man.disklabel.8; regressions: The biggest casualty of the
introduction of GEOM appears to be the disklabel utility. The
<option>-r</option> option gives unpredictable results in most
cases now and should be removed or fixed. Work is planned for a
new unified interface for modifying labels and slices, however
this should not preclude disklabel from being fixed.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>Documentation:</para>
<itemizedlist>
<listitem>
<para>The manual pages, Handbook, and FAQ should be free from
content specific to &os; 4.<replaceable>X</replaceable>, i.e. all
text should be equally applicable to &os;
5.<replaceable>X</replaceable>. The installation section of the
handbook needs the most work in this area.</para>
</listitem>
<listitem>
<para>The release documentation needs to be complete and accurate
for all Tier-1 architectures. The hardware notes and
installation guides need specific attention.</para>
</listitem>
<listitem>
<para>If &os; 5.1 is not the branch point for &t.releng.5; then the
Early Adopters Guide needs to be updated. This document should
then be removed just before the release closest to the &t.releng.5;
branch point.</para>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="schedule">
<title>Schedule</title>
<para>If branching &t.releng.5; at the 5.1 release is paramount, 5.1 will
probably need to move out by at least 3 months. The schedule would
be:</para>
<itemizedlist>
<listitem>
<para>Jun 30, 2003: KSE and SMPng feature freeze</para>
</listitem>
<listitem>
<para>Aug 4, 2003: 5.1-BETA, general code freeze</para>
</listitem>
<listitem>
<para>Aug 18, 2003: 5.1-RC1, &t.releng.5; and &t.releng.5.1; branched</para>
</listitem>
<listitem>
<para>Aug 25, 2003: 5.1-RC2</para>
</listitem>
<listitem>
<para>Sept 1, 2003: 5.1-RELEASE</para>
</listitem>
</itemizedlist>
<para>Taking an incremental approach might be more beneficial. Releasing
5.1 in time for USENIX ATC 2003 will provide a wide audience for
productive feedback and will keep &os; visible. In this scenario, 5.1
should offer a significant improvement over 5.0 in terms of bug fixes
and performance. Lockdowns and improvements to the storage subsystem
and scheduler should be expected, the NEWCARD/OLDCARD issues should be
addressed, and all known bugs and regressions from the 5.0 errata list
should be fixed. KSE and other SMPng tasks that cannot finish in time
for 5.1 should also not reduce the stability of the release. The
schedule for this would be:</para>
<itemizedlist>
<listitem>
<para>May 5, 2003: 5.1-BETA, general code freeze</para>
</listitem>
<listitem>
<para>May 19, 2003: 5.1-RC1, &t.releng.5.1; branched</para>
</listitem>
<listitem>
<para>May 27, 2003: 5.1-RC2</para>
</listitem>
<listitem>
<para>Jun 2, 2003: 5.1-RELEASE</para>
</listitem>
<listitem>
<para>Jun 30, 2003: KSE and SMPng feature freeze</para>
</listitem>
<listitem>
<para>Sept 1, 2003: 5.2-BETA, general code freeze</para>
</listitem>
<listitem>
<para>Sept 15, 2003: 5.2-RC1, &t.releng.5; and &t.releng.5.2; branched</para>
</listitem>
<listitem>
<para>Sept 22, 2003: 5.2-RC2</para>
</listitem>
<listitem>
<para>Sept 29, 2003: 5.2-RELEASE</para>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="future">
<title>Post &t.releng.5; direction</title>
<para> As with all -STABLE development streams, the focus should be bug
fixes and incremental improvements. Just like normal, everything
should be vetted through the &t.releng.head; branch first and committed to
&t.releng.5; with caution. As before, new device drivers, incremental
features, etc, will be welcome in the branch once they have been proven
in &t.releng.head;.</para>
<para>Further SMPng lockdowns will be divided into two categories, driver
and subsystem. The only subsystem that will be sufficiently locked
down for &t.releng.5; will be GEOM, so incrementally locking down device
drivers under it is a worthy goal for the branch. Full subsystem
lockdowns will have to be fully tested and proven in &t.releng.head; before
consideration will be given to merging them into &t.releng.5;.</para>
</sect1>
</article>
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