View source for Real Time Working Group

== Real-Time Working Group ==

This page will collect the publicly available information about the activities of the real-time working group. 

=== Charter ===

The real-time working group will work to improve the real-time
capabilities of the Linux operating system to address the range
of real-time requirements for consumer electronics devices. 

The working group will establish the real-time requirements for
consumer electronics devices and evaluate the suitability of 
candidate architectures and implementations to satisfy those
requirements. 

=== Scope ===

The scope of the real-time working group will include the kernel 
as well as user-level libraries (e.g, Native POSIX Thread Library) 
that collectively provide the run-time environment with suitable
real-time characteristics. In addition, the group will also focus
on tools for timing analysis. 

The working group may address the real-time requirements through 
the following technology areas: 

# Improved real-time capabilities for applications that use the
the POSIX real-time features already available in Linux.

2. New POSIX real-time features that are not currently available
in Linux. 

3. New resource management techniques (such as those offered by 
the the notion of resource kernel) that extend beyond the 
basic preemptive priority resource management. 

4. Preservation of real-time capabilities for applications that
use the rich functionality offered by Linux (e.g., applications
that use file systems or networking should also be able to 
achieve real-time behavior). 


5. Tools to understand and debug the timing behavior of systems.

6. Interaction of real-time behavior with power-management. 

=== Organization ===

The working group is chaired by Manas Saksena. You can contact him directly at manas.saksena@timesys.com. 

=== Implementations ===

The following patches have been submitted to the RTWG mailing list.  

==== Interrupt Priorities + Interrupt Threads + Soft IRQ Threads ====

This patch implements a priority based interrupts that includes interrupt priorities, 
interrupt thread, and softirq threads. The patch is for 2.6.0 ppc (IBM [[PowerPC]] 405). 

This patch was submitted by Norio Nakagawa (Fujitsu). 

[[Media:linux-2.6.0-PriorityBasedIntr.diff]]

==== Interrupt Threads + Soft IRQ Threads ====

This patch that implements "irq-threads" feature on 2.6.4. The feature is enabled by the 
option CONFIG_IRQ_THREADS (which depends on the option CONFIG_SOFTIRQ_THREADS). Both 
options depend on CONFIG_PREEMPT. This patch is only for x86, but it is relatively
easy to port it to other architectures.

When the feature is turned on, a kernel thread is created for each
IRQ (unless, the ISR is installed with SA_NOTHREAD option). In the
main IRQ handling function, instead of directly executing the
installed handler, the code wakes up the corresponding kernel
thread, which executes the ISRs. The flag SA_NOTHREAD can be used
at the time of installing an ISR to tell the kernel that the ISR
should not be executed in thread context. The patch uses this option
for various input drivers (keyboard, mouse, etc.) since they do not
function well when run in thread context.

The patch also turns all softirq processing into thread context as
well (otherwise, it will not make much sense).

The patch was submitted by Manas Saksena (TimeSys).  The implementation was done by Scott Wood (TimeSys).

[[Media:linux-2.6.4-irq-threads.patch]]