Tuesday Sep 08, 2009

Java RTS 2.2 Early Access 2 Released

Sun recently announced the availability of a second edition of its Java Real-Time System (Java RTS) version 2.2 Early Access.  In a previous blog post, many of the important new features of this release were highlighted.  But I felt compelled to jot down a few additional words, not only because there's a newer version of the software to evaluate, but because there's one interesting component that deserves a little more exposure.

I spent some time today speaking with my compadre, Eric Bruno, author of Real-Time Java Programming: With Java RTS.  He clued me in on the fact that our engineers have performed the daunting task of backporting the JDK 7 client compiler onto Java RTS 2.2.  The engineering team is particularly proud of this feat, and ought to be.  It not only enhances Java RTS performance, it also enables them to better stay in lock step with the latest client hotspot VM developments, something the latest Java SE 6 releases may not entirely do.  For some insight into the engineering trade-offs associated creating this latest version of Java RTS, check out Roland Westerlin's entry.

You can find further information about Java RTS here.  And you can download a version of the software for evaluation here.

Cheers.

Wednesday Jun 10, 2009

Early Access version of Java RTS 2.2 Released

Just in time for the start of JavaOne 2009, Sun released the latest version of its real-time Java platform, Java RTS 2.2, in early access form.  New features of this release include but are not limited to:

  • OS Platform support for Solaris 10 (x86 and Sparc - Update 5 & 6), Red Hat MRG 1.1 and  SUSE Linux Enterprise Real-Time 10 (SP2 Update 4)
  • 64-bit support for the three operating systems mentioned above. In addition, 32-bit support continues to be supported.
  • Faster throughput. Java RTS 2.2 utilizes a new dynamic (JIT) compiler targeted for Java SE 7 which contains several performance improvements including a new register allocator.
  • TSV (Thread Scheduling Visualizer) enhancements.
  • NetBeans plug-in support for Java RTS and TSV. 
  • New Initialization-Time-Compilation (ITC) options including the ability to wild card a set of methods vs listing single methods and support for specifying compilation based on thread type.
  • Auto-tuning and startup improvements made to the Real-time Garbage Collector (RTGC).
  • New documentation including a Java RTS Quick Start Guide to get new users started quickly with minimum programming and configuration.

A 90-day evaluation is available here: http://java.sun.com/javase/technologies/realtime/index.jsp.  For more detailed information on OS support and new functionality, check out the 2.2 Release Notes.

Wednesday Jan 14, 2009

Overhead in Increasing the Solaris System Clock Rate

In a previous entry entitled Real-Time Java and High Resolution Timers, we discussed how Sun's Java Real-Time System requires access to timers with a resolution greater than the default 10ms to do anything really interesting.   It was also stated that most modern processors have an APIC or Advanced Programmable Interrupt Controller which supports much finer-grained clock tick rates.

Unfortunately there are many instances where a system does indeed contain an APIC, but it is not exposed by the BIOS.  Furthermore, we've found that some of the embedded, low-power x86-based processors do not contain an APIC at all.  For an example, take a look at the AMD Geode LX 800 based fit-PC Slim.

So if you wanted to utilize higher resolution timers for this class of system, you'd have to resort to alternative methods.  Solaris and OpenSolaris provide two /etc/system parameters called hires_tick and hires_hz to facilitate increasing your default system clock tick.  By adding the following line to /etc/system, you'll increase the system clock tick rate from the default of 100 per second to 1,000 per second, effectively changing the clock resolution from 10ms to 1ms.

   set hires_tick=1

If you want to further increase the clock resolution, you can do so via the hires_hz system tunable parameter.  Although formally unsupported, it does work.   In order to, for example, increase the clock tick rate to 10,000, add this to /etc/system:

    set hires_tick=1
    set hires_hz=10000

To achieve the desired effect above, you must include both the hires_tick assignment in addition to setting the hires_hz parameter.

These modifications do not come without side-effects, and depending upon the hardware in question and the granularity of the desired timer resolution, they could be significant.  In short, it takes additional CPU cycles to field all those timer interrupts.  So I thought it'd be interesting to see what effect changing the clock tick rate had on two separate systems.   Here they are:

 System  fit-PC Slim
 Panasonic Toughbook CF-30 (Revision F)
 CPU  AMD Geode LX 800 (500 Mhz)
 Intel Core 2 Duo L7500 1.60GHz
 OpenSolaris Version
 snv_98  snv_101b

The measuring tool used for this simple experiment is vmstat(1m).  Solaris aficionados will likely point out that there are much more accurate alternatives, but I think vmstat(1m) gives a decent feel for what's going on without having to expend a whole lot of extra energy.  In particular we'll look at the following fields returned by issuing a 'vmstat 5', and picking one of the interim samples:

  • in - interrupts per second
  • us - percentage usage of CPU time in user space
  • sy - percentage usage of CPU time in system space
  • id - percentage usage of CPU time idling

The sum of (us + sy + id) should approximate 100%.  The table below shows sample vmstat output on various clock tick settings for our two hardware platforms.

Clock tics/sec
 100
 1000  10000  100000
/etc/system settings
 none (default)
 set hires_tick=1
set hires_tick=1
set hires_hz=10000
set hires_tick=1
set hires_hz=100000
vmstat(5) sample fit-PC
 in: 201
 us: 0
 sy: 1
 id: 99
 in: 2001
 us: 0
 sy: 5
 id: 95
 in: 19831
 us: 0
 sy: 43
 id: 57 
n/a

vmstat(5) sample CF-30

 in: 471
 us: 0
 sy: 0
 id: 99
 in: 2278
 us: 0
 sy: 1
 id: 99
 in: 20299
 us: 0
 sy: 5
 id: 95
 in: 200307
 us: 0
 sy: 21
 id: 79

Notes/Conclusions:

  • The vmstat(5) was let run for about a minute.  The output above shows one of the typical 5 second samples.  The other 5 second samples are almost identical.
  • The user (us) CPU time numbers give us a reasonable idea that these systems were predominantly in an idle state when being sampled.
  • The number of interrupts serviced per second is directly proportional to the clock tick rate.
  • And of course, the larger the number of interrupts, the more system CPU time is required.
  • The amount of overhead taken up by increasing the clock rate is a function of system capability.  The CF-30 not only has a much faster processor, it also has two cores to share the interrupt load.  As such it could accommodate a much higher clock tick rate.  For the fit-PC, performance is impacted profoundly even at modest clock tick rates.

Wednesday Jul 23, 2008

Fast Booting Solaris

A veteran Java ONE keynote presenter, Perrone Robotics has developed some real interesting technologies which take the concept of using autonomous (i.e. unmanned) vehicles to a whole new level.  One of their key ingredients is the MAX software platform which utilizes common commercially available components to enable Perrone to very quickly and cost-effectively retrofit nearly any vehicle in short order.


The MAX robotics platform runs on a (roughly 4" x 6") low-power PC board atop Solaris and Sun's Java Real-Time System (Java RTS).  This combination gives Perrone the ability to leverage the huge Java development community, and assures that their critical software components behave in a predictable and deterministic fashion.

During the Java ONE 2007 conference, I was speaking with Paul Perrone about the notion of creating a minimized version of Solaris over which his platform might run.  The helicopter pictured above, boots from a relatively small (4-8Gb)  IDE flash drive, where standard Solaris takes up a substantial chunk.  It leaves them precious little space to collect valuable information like telemetry or terrain data.  Paul asked to revist this idea for a future project.  That's where we left off.

Not that we've ignored them since, but it wasn't until a year later that small Solaris reared its head again.  In addition to saving space, their main interest in this environment was in seeing how much faster Solaris might boot up.  The ability to be fully functional from power-up in as short a time as possible is of critical importance.

So before investigating what advantages there might be, let's provide some background information:

Hardware

Two separate systems were used, and for argument's sake, represent two ends of the x86 compute spectrum. 


Embedded Profile
Modern Profile 
System iGologic i84810
Panasonic Toughbook CF-30 (Rev. F)
CPU 1GHz Celeron M
Core 2 Duo L7500 1.60GHz
RAM 512MB 1GB
Disk 4GB Flash IDE Drive
Solid State SATA Drive

Operating Systems

Minimal configurations were created for Solaris 10 08/07 (Update 4) and OpenSolaris Nevada build 93.  These configurations boot entirely into RAM and consume less than 100MB ramdisk space.  With a little more effort they can be may significantly smaller.  The original blog post describing the environment is here.   You can download the framework for these hardware/OS combinations here, and can get a feel for the build environment by taking a look at this README.

Definitions

Within the context of this discussion, here are the key terms along with their meanings.

Total Boot Time: This is the time it takes from power-up till a user is prompted to log in.  Typically for a full Solaris installation, the windowing system must first start up and present the user with a login screen.  In a minimal Solaris environment, there is no windowing system.  Instead, the total boot time is defined as the time it takes from power-up till a user is prompted with the console login: prompt.

POST Time: POST or Power On Self Test is the time taken by the system at pre-boot to handle things like diagnostics,  BIOS and device initialization.  For this discussion, we'll define POST time as the time it takes from power-up until the user is presented with a GRUB boot menu.  We call out this segment of the total time because in many cases we are at the mercy of the PC/BIOS manufacturer and can't overly influence how quickly or slowly this proceeds.

Solaris Boot Time: The time it takes from being presented with a GRUB boot menu till a Solaris user is prompted to log in.  Again, depending upon whether a windowing system is configured or not, this may represent the time it takes to be prompted with a login screen or console login: prompt respectively.  This represents the segment of time that we can influence.

We can conclude from these definitions that:

   Total Boot Time = POST Time + Solaris Boot Time

Results

Embedded Profile: iGoLogic i84810 system 

OS
Post Time
Solaris Boot Time
Total Boot Time
 Solaris 10 08/07
13 sec
26 sec
39 sec
 OpenSolaris Nevada Build 93
13 sec
18 sec
31 sec 

Modern Profile: Panasonic Toughbook CF-30

OS POST Time
Solaris Boot Time
 Total Boot Time
 Solaris 10 08/07
 6 sec
 18 sec
 24 sec
 OpenSolaris Nevada Build 93
 6 sec
 9 sec
 15 sec

Conclusions/Notes

1. These times were taken by hand with the stopwatch feature on my Timex.  If anything, the times might be slightly shorter than actually recorded as there is a human delay in reacting to seeing the necessary prompts.  I ran the tests several times, and the same numbers consistently appear.

2. The version of the OS appears to matter a lot, as OpenSolaris nvx_93 boots up nearly twice as fast as Solaris 10 U4 on the same hardware.

3. The type of I/O device subsystem seems to be a big factor too.  For example, by switching out the IDE Flash Drive with a 5400 RPM IDE hard disk, i84810 total boot time decreased by about 6 seconds for both Solaris 10 and OpenSolaris. 

4. The minimal Solaris environment is currently only available in 32-bit mode.

5. With relative ease, Solaris can be configured to boot in less that 10 seconds on modern x86 hardware.  My unofficial record stands at 9 seconds (or slightly less).   No doubt it could boot faster on more robust hardware (eliminating POST time).  Any takers?

Tuesday Jun 17, 2008

Real-Time Java in a Zone

As is often the case, Sun's technologies and offerings are being applied in ways which we hadn't necessarily anticipated.  Yet another example has reared its head in the govenrment/military space where customers have expressed interest in using Sun's Java Real-Time System with Solaris Trusted Extensions.  As it stands right now, Java RTS will neither operate nor install within the confines of such an environment.  Let's investigate why this is so, and see what current opportunities there are for working around this shortcoming.

So what is it that causes Trusted Extensions and Java RTS not to play together nicely?   It happens to revolve around Trusted Extension's extensive usage of Solaris zones to limit access between differing security levels.  Solaris packages must be specifically configured to accommodate zones, which has yet to formally take place with Java RTS.  As zones are a core component of Solaris, we can, for the sake of simplicity, just use standard Solaris to demonstrate how we can work around this temporary limitation.  These modifications should apply to Trusted Extensions just as well.   To get Java RTS to work within a zone, follow these steps:

1. Install the Java RTS cyclic driver (only) in the global zone.

global# pkgadd -d . SUNWrtjc

Processing package instance <SUNWrtjc> from </cyclic/src/packages_i386>
## Installing package <SUNWrtjc> in global zone

Java Real-Time System cyclic driver(i386) 2.1.0,REV=2008.06.13.16.10
Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
Use is subject to license terms.
Using </> as the package base directory.
## Processing package information.
## Processing system information.
   5 package pathnames are already properly installed.
## Verifying package dependencies.
## Verifying disk space requirements.
## Checking for conflicts with packages already installed.
## Checking for setuid/setgid programs.

This package contains scripts which will be executed with super-user
permission during the process of installing this package.

Do you want to continue with the installation of <SUNWrtjc> [y,n,?] y

Installing Java Real-Time System cyclic driver as <SUNWrtjc>


2. Create a zone called 'rtjzone':
global# mkdir -p /zone
bash-3.00# zonecfg -z rtjzone
rtjzone: No such zone configured
Use 'create' to begin configuring a new zone.
zonecfg:rtjzone> create
zonecfg:rtjzone> set zonepath=/zone/rtjzone
zonecfg:rtjzone> verify
zonecfg:rtjzone> commit
zonecfg:rtjzone> exit
global# zoneadm list -vc
  ID NAME             STATUS     PATH                           BRAND    IP
   0 global           running    /                              native   shared
   - rtjzone          configured /zone/rtjzone                  native   shared
global# zoneadm -z rtjzone install
Preparing to install zone <rtjzone>.
Creating list of files to copy from the global zone.
Copying <6984> files to the zone.
Initializing zone product registry.
Determining zone package initialization order.
Preparing to initialize <1074> packages on the zone.
Initialized <1074> packages on zone.
Zone <rtjzone> is initialized.
Installation of <1> packages was skipped.
The file </zone/rtjzone/root/var/sadm/system/logs/install_log> contains a log of the zone installation.


3.  Modify the zone to allow access to the cyclic device, and to allow additional privileges

global# zonecfg -z rtjzone
zonecfg:rtjzone> set limitpriv=default,proc_priocntl,proc_lock_memory,proc_clock_highres
zonecfg:rtjzone> add device
zonecfg:rtjzone:device> set match=/dev/cyclic
zonecfg:rtjzone:device> end
zonecfg:rtjzone> verify
zonecfg:rtjzone> commit
zonecfg:rtjzone> exit

global# zoneadm -z rtjzone reboot
Note:  One privilege that is useful with Java RTS is sys_res_config.  This is typically used to assign a real-time process to a processor set.  Unfortunately zones cannot currently be given this privilege.  You can however, from the global zone, assign a processor set to a zone, which might be a reasonable workaround.

4.  Get a copy of the SUNWrtjv package and modify it so that it will install in a zone.  The postinstall script and postremove script must replaced with those provided by these hyperlinks just mentioned.

rtjzone# cd /scratch
rtjzone# ls
SUNWrtjv	postinstall	postremove
rtjzone# cp postinstall SUNWrtjv/install/
rtjzone# cp postremove SUNWrtjv/install/

5. Modify the SUNWrtjv pkgmap file with the appropriate sizes, checksums and last access dates.  The source code for a sample C program, called pkgmap_info, which prints out the necessary information, can be found here.

rtjzone# cd SUNWrtjv
rtjzone# grep post pkgmap 1 i postinstall 5402 42894 1194344457 1 i postremove 2966 34854 1194344457 rtjzone# cp pkgmap_info.c /tmp rtjzone# cc -o /tmp/pkgmap_info /tmp/pkgmap_info.c rtjzone# cd /scratch/SUNWrtjv/install/ rtjzone# /tmp/pkgmap_info postinstall postinstall 5820 9488 1213727841 rtjzone# /tmp/pkgmap_info postremove postremove 3092 45039 1213727538
Replace the postinstall and postremove entries in the pkgmap file with those produced by the pkgmap_info program.  You cannot simply use the example data above because the last access times will not match.  Doing so will cause the install to fail.


6. Install the Java RTS SUNWrtjv package inside the zone.

rtjzone# cd /scratch
rtjzone# pkgadd -d . SUNWrtjv

Processing package instance <SUNWrtjv> from </scratch>

Java Real-Time System runtime environment(i386) 1.5.0_13_Java-RTS-2.0_01-b08_RTSJ-1.0.2,REV=2007.11.06.12.47
Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
Use is subject to license terms.

Where should this package be installed? (/opt): /opt

To achieve predictable temporal behavior, the Java Real-Time System
must be granted access to a number of privileged Solaris resources.
By default, access to these privileged resources is only granted to
the superuser (root). They can also be granted to additional users
by creating a rights profile, that is, a collection of authorizations,
that can later be assigned to an administrative role or directly
to a user.

As part of this package installation, a local 'Java Real-Time System User'
rights profile can be created on this machine.
This rights profile should NOT be created if such an action conflicts
with your computer security management policies. If unsure, contact
your system administrator or your computer security manager.
Also refer to the product's release notes for further details regarding
the privileges required by the Java Real-Time System.

Should a local 'Java Real-Time System User' rights profile be created? [y,n] (no): y
Using </opt> as the package base directory.
## Processing package information.
## Processing system information.
## Verifying package dependencies.
## Verifying disk space requirements.
## Checking for conflicts with packages already installed.
## Checking for setuid/setgid programs.

This package contains scripts which will be executed with super-user
permission during the process of installing this package.

Do you want to continue with the installation of <SUNWrtjv> [y,n,?] y

...

## Executing postinstall script.
Creating the 'Java Real-Time System User' rights profile.

Refer to the 'System Administration Guide: Security Services'
documentation for further information regarding the way to assign the
'Java Real-Time System User' rights profile to users, groups, or
administrative roles using the Solaris Management Console, smc(1M) or
the usermod(1M), groupmod(1M) and rolemod(1M) commands.


Installation of <SUNWrtjv> was successful.


6.  Try running a real-time Java application in the zone.

rtjzone# /opt/SUNWrtjv/bin/java -version
java version "1.5.0_13"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_13_Java-RTS-2.0_01-b08_RTSJ-1.0.2)
Java Real-Time System HotSpot(TM) Client VM (build 1.5.0_13-b08, mixed mode)


We hope to more formally support Solaris zones usage with Java RTS in the future.  In the interim this workaround can help you get started.  Many thanks to Jim Clarke, who did the lion's share of the legwork to find this solution.

Thursday Jan 31, 2008

Good Things Come To Those Who Wait

Java RTS 2.1 EA (Early Access) marks the arrival of a commitment made some time back, namely that Sun would provide a version of the Java Real-Time System for Linux.  Perhaps to some, it was long time in the making, but in fact there are at least 2 good reasons why a Linux version wasn't available till now:

  1. Until recently, there was no standard Linux release/kernel which had true real-time support.  Typically the versions available were non-standard and did not constitute any considerable volume.  Mainstream Linux distributions are only now incorporating the necessary real-time underpinnings.
  2. Porting the Java Real-Time System VM to additional platforms is non-trivial.

Support and testing for Java RTS 2.1 EA at this time is limited to the currently shipping SUSE Linux Enterprise Real Time10 platform and the upcoming Red Hat Enterprise MRG 1.0 release.  It is however possible that other versions of Linux could run Java RTS 2.1 EA as it utilizes the real-time POSIX programming interface.  At minimum they would require a 2.6.21 kernel or greater and a glibc of 2.5 or greater.  In addition, the latest RT patch would also be needed.

This announcement pertains only to Linux, but of course a 2.1 EA version for both Solaris x86/x64 and Sparc will be shortly forthcoming. In the interim, a version of Java RTS 2.0 update 1 is readily available.  Documentation for both Java RTS 2.0 and 2.1 EA can be found here.

Regardless of platform, an evaluation version of the software is available for download at the Java RTS download page.

 

Wednesday Dec 19, 2007

Java RTS 2.0 Update 1 Released

After blogging about the relationship between high resolution timers and Java RTS, a comment was posted by a reader stating that they couldn't use Java RTS 2.0 with the latest Solaris 10 update.  Unfortunately that reader was correct.

At the time of the post, Sun had released Solaris 10 Update 4, while Java RTS 2.0 would only support Solaris 10 update 3.  To further exacerbate the situation, once Sun releases a new version of Solaris, they do their best to encourage users to use the latest version by making it difficult (if not impossible) for them to locate previous update versions.

There is a dependency between the aforementioned high resolution timer interface and Solaris which is update specific.  We're working to rectify this situation, but as the process behind Solaris is deliberately bureaucratic, this might take a while.  In the interim we'll need to keep in better lock step with Solaris releases.

On November 27, Java RTS 2.0 update 1 was released: 

  • It supports the latest Solaris 10 update (called 08/07 or update 4)
  • Support for Java SE has been updated to Java SE 5 update 13
  • A new Java RTS DTrace Provider is available
  • Other enhancements are listed here

 

Monday Oct 15, 2007

General Purpose Always Wins ... Why Not for the Real-Time Market Too?

The brief but brilliant era of computing has seen companies come and go, many relegated to the ash heap of history because they failed to heed this simple rule:  
 
  In the long run general purpose solutions will always win out over specialized proprietary ones. 
 
As a long time employee of Sun Microsystems, I've witnessed firsthand the effects, both positive and negative, that this law has had on my company.  Sun can attribute it's initial meteoric rise to the fact that it offered a viable alternative to the popular minicomputer platform of the day.  The first Sun workstations were built from commercial off-the-shelf components, and although nearly equal in performance to the minicomputer, they were so much more affordable that they became good enough.  And of course over time, as Moore's law might dictate, those initial deficiencies quickly dissipated, and in fact surpassed traditional minicomputer capabilities.
 
Somewhere along the line Sun lost sight of this ideal and began incorporating more proprietary technology into their products.  At first the strategy appeared to be successful as Sun was well positioned to reap huge benefits during the Internet bubble.  Meanwhile, low-cost general purpose servers were continuously improving.  When the bubble burst they in turn became good enough alternatives to the powerful but costly Sun servers.  The resulting decline of Sun was rapid, and it's taken the better part of a decade for us to recover.   This story has been told -- and will continue to be again and again -- for those refusing to learn this lesson.  A professor of mine once told me, "If there's anything we've learned from history, it's that we haven't learned anything from history".

When markets mature, even those where technology is paramount, economic considerations dominate. General purpose systems scale on every dimension (unit, management, training and integration costs) whereas proprietary systems do not.  A switch to more standard components should in no way be construed as stifling innovation.  Rather, general purpose systems help create new innovation by building from common elements economically appealing in their own right, and presumably even more economically beneficial once combined.1

[1] The above paragraph was taken in bits and pieces from an email exchange with Dave Hofert, Java Embedded and Real-Time Marketing Manager.  His points were so compelling I couldn't help myself.

Real-time industrial controllers could be the next market ripe for disruption.  Admittedly this is an entrenched and conservative lot.  But the economics of general purpose computing cannot be denied.  As organizations strive to further eliminate cost out of their system, revisiting usage and deployment of industrial controllers, typically via custom proprietary PLCs, is falling under review.  Consequently, at the behest of one of the world's largest industrial corporations, Sun has partnered with iGoLogic, a systems integrator, and Axiomtek, an industrial PC board manufacturer, to create the real-time controller platform pictured below.
 
Among others, here are some of the compelling benefits of this platform: 

  • It's based on standard x86 hardware.  The motherboards aren't much larger than a postcard, are energy efficient, and yet have PC class processing power.  The number of competing manufacturers in this space eliminates vendor lock-in and insures price sensitivity and further rapid innovation.
  • Real-time applications are developed using Sun's Java Real-Time System, enabling you to leverage the largest development community on the planet.  Obscure development languages and highly specialized environments are longer needed.
  • Industrial Networking Protocols (e.g PROFIBUS, EtherCAT) are easily migrated to this platform, partly because of the wealth of development tools available.
  • The system utilizes an IDE flash drive from Apacer.  In addition to eliminating the moving parts associated with a traditional disk drive, it consumes less power and makes the system more resistant to shock and vibration.  Overcoming the longevity limitations of flash memory, Apacer has done some interesting work on wear leveling algorithms effectively extending the lifetime of the flash device well past the expected lifetime of the industrial controller.

 
Let this be our first salvo fired over the proprietary industrial encampment.  We believe the opportunity is immense, but also understand that to achieve any measure of success, partnering with organizations who are truly experts in this arena is critical.  If you think you can add further value, we'd love to talk.

Tuesday Jun 19, 2007

Real-Time Java and High Resolution Timers

Any modern x86/x64 processor worth its salt comes equipped with an Advanced Programmable Interrupt Controller, or APIC.  Among the features that an APIC provides is access to high resolution timers.  Without such capability, the default interrupt source for timer and cyclic operations has a precision on the order of 10 milliseconds -- hardly fine-grained enough for any serious real-time work.

The cyclic subsystem, introduced in Solaris 8, gives Solaris the capability to support high resolution timers.  The Sun Java Real-Time System version 2.0, available for Solaris on both x86 and Sparc platforms, includes an additional package called SUNWrtjcJava Real-Time System cyclic driver.  This package exposes an interface to the cyclic subsystem, normally only available to the kernel.  For those already familiar with Sun's Java RTS, you've no doubt noticed that you either need to run as superuser or assign a set of fine-grained privileges to an ordinary user account. (sys_res_config, proc_priocntl, proc_lock_memory and proc_clock_highres).  The proc_clock_highres privilege gives access to those timers.

Originally developed on an AMD Athlon-based PC, I recently moved a Real-Time Java project over to my Toshiba Tecra A1 laptop running the same version of Solaris and Java RTS.  With the goal of getting in a little development time during a long flight, that migration suddenly casued timings to be all wrong.  Why, might you ask, would moving an application from one seemingly identical Solaris environment to another cause this unusual behavior?  Turns out that even though the laptop, a Pentium 4M based system, has an APIC, it was never exposed by the laptop BIOS.  In this scenario, regardless what you do from a Solaris perspective, you'll never get access to the high-res timers. 

This phenomenon appears to be most prevelant in laptops.  As they account for about 50% (or more?) of PCs sold today, developers have a realistic chance of running into this situation.  You can issue this magic Solaris incantation to determine if your system has high-res timer support:

   # echo "psm_timer_reprogram::print"  | mdb -k

If anything but 'apic_timer_reprogram' is then displayed, your machine has no exposed APIC, and is probably unsuitable for Java RTS.  In some cases the BIOS may be configurable with regards to APIC support; in many others it is simply not available.

In the absence of an APIC, there is the potential to improve the high-resolution timing by setting the following tunable in /etc/system:

   set hires_tick=1

Following a reboot, this would change the clock tick frequency from 100 to 1000 ticks per second. This frequency can then be further tuned by setting the hires_hz tunable to the desired value:

   set hires_hz=10000

The default value is 1000 ticks per second; higher values are not officially supported.

Note that tuning your machine in this way does not come without cost.  It is likely to degrade overall performance, as the system will need to spend a larger proportion of time handling the larger frequency of clock interrupts.1

   [1] Thank you  Christophe Lizzi for your explanation of the problem and potential workaround.
 

 

Monday Jun 11, 2007

Audio Transcript and Slides Available for "Real-Time Java Meets Wall Street"

Better late than never ...

As Promised, you can find the audio transcript for the Java ONE 2007 technical session TS-1205: The Sun  Java Real-Time System Meets Wall Street at the aforementioned link.  The slide deck should also be available there, or can be downloaded here.
 

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Jim Connors

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