Dear

Now I am studying the scheduler design issue of DROPS including Fiasco and L4Linux.
In the reference document, "L4Linux Porting Optimizations", it said that

"   In an L4Linux system two schedulers are active. One is in the L4 kernel scheduling all L4
threads including L4Linux processes. The L4 scheduler uses static priorities and schedules
threads with the same priority round-robin.
   
    The other scheduler is in the Linux server, deciding which Linux process to run next. L4Linux
is designed in a way that from the view of the Linux server multiple user processes can be
running in the L4 system. Furthermore, the Linux scheduler can only consider those processes
that are blocked in the server. Consequently, the Linux server needs to distinguish between user
processes being served by the Linux server and the ones running."

For the behavior of the scheduler in L4Linux, I got some questions below.

  1. In L4Linux, the process/thread will map to several L4 Threads. How the scheduler in the Linux Server considers user processes in L4Linux whether to execute in L4 system ? According to the document, does L4Linux scheduler only control the user process whether block or not?

  2. Based on the L4Linux source code from currently SVN, the behavior of schedule() function (kernel/sched.c line 4546) is
    => If next != prev, call context_switch() function
    => In context_switch() function (kernel/sched.c Line 2649), it calls architecture dependent function switch_to()
    => In switch_to() function (arch/l4/include/asm/arch-arm/system.h Line 222), it calls l4x_switch_to() function and   __switch_to() function
    => In l4x_switch_to() function (arch/l4/kernel/arch-arm/dispatch.c Line 170), it logs the message to Trace Buffer of Fiasco and set l4x_current_process
    => In __switch_to() function (arch/l4/kernel/arch-arm/switch_to.S Line 5), it store the registers to CPU context of thread_info and load all regs saved previously

    Based on the source code analysis, it seems that when the L4Linux scheduler decide to do the context switch, the architecture dependent function __switch_to() will do the register restore and load. According to the document, I think the behavior here should set the corresponding thread status of prev and next user process to block or unblock these L4 threads. But here it does low level register restore and reload operations to change the current running process directly. It confuses me. Can anyone give me any ideas to address this?  

Thanks a lot!

Best Regards,
Sean