CS533 Concepts of Operating Systems Class 7 Integrated Task and Stack Management

CS533 - Concepts of Operating Systems 2 Questions  What do these terms mean? o process, thread, kernel-level thread, user-level thread, fiber? o user-level thread stack, user stack, kernel stack? o Address space?

CS533 - Concepts of Operating Systems 3 Questions  How might a user-level thread library support synchronous I/O calls for its threads without losing control of the CPU due to blocking? o How does this approach behave during page-faults? o Does this matter? o Can it deal with preemptions?  Do user-level thread libraries do “stack ripping”?

CS533 - Concepts of Operating Systems 4 Questions  In what way are user-level threads “faster” than kernel-level threads? o Aren’t we just layering abstractions on abstractions?  Why can’t you do preemptive user-level thread scheduling without special kernel support? o Does this mean you can only do sequential task management? o Can you do cooperative task management? o How?

CS533 - Concepts of Operating Systems 5 Questions  Is synchronization needed for cooperative user-level scheduling on uniprocessors? o What precautions must you take? o Is synchronization needed on multiprocessors?  How are synchronization operations such as spin- locks and semaphores implemented, i.e., how do you spin and how do you block? o For user level threads? o For kernel level threads?

CS533 - Concepts of Operating Systems 6 Questions  What stack management model do most OS kernels export? o How are I/O and page faults events handled?  What differences are there between virtual CPUs (threads) and real CPUs (hardware)? o How are I/O and page fault events handled? o How is time managed?  What similarities do kernel-provided scheduler activations have to hardware-provided interrupts?

CS533 - Concepts of Operating Systems 7 Questions  What synchronization-related issues do you have to worry about when writing an interrupt handler? o What about a scheduler activation handler?  Why must the user-level thread library be reentrant? o How is its pattern of entry points and synchronization concerns similar to OS kernel code?

CS533 - Concepts of Operating Systems 8 Questions  How might a scheduler activation handler deadlock? o What would a prevention-based solution look like? o What problems would it have? o What would a recovery-based solution look like? o What problems would it have?  Why does the kernel delay delivery of a second page-fault SA until the first page-fault SA on the same address has completed?

CS533 - Concepts of Operating Systems 9 Questions  What happens immediately following I/O completion if the calling thread still has more kernel code to execute?  In what ways do scheduler activations mix manual and automatic stack management models? o Are they a translation point / boundary between the two models?

CS533 - Concepts of Operating Systems 10 Reminder  Class 8 presenters o Discuss your presentation plans with me ahead of time o Mail me the final version of your slides BEFORE the class