-*- text -*-
+Godmar says:
+
+- In Project 2, we're missing tests that pass arguments to system calls
+that span multiple pages, where some are mapped and some are not.
+An implementation that only checks the first page, rather than all pages
+that can be touched during a call to read()/write() passes all tests.
+
+- In Project 2, we're missing a test that would fail if they assumed
+that contiguous user-virtual addresses are laid out contiguously
+in memory. The loading code should ensure that non-contiguous
+physical pages are allocated for the data segment (at least.)
+
+- Need some tests that test that illegal accesses lead to process
+termination. I have written some, will add them. In P2, obviously,
+this would require that the students break this functionality since
+the page directory is initialized for them, still it would be good
+to have.
+
+- There does not appear to be a test that checks that they close all
+fd's on exit. Idea: add statistics & self-diagnostics code to palloc.c
+and malloc.c. Self-diagnostics code could be used for debugging.
+The statistics code would report how much kernel memory is free.
+Add a system call "get_kernel_memory_information". User programs
+could engage in a variety of activities and notice leaks by checking
+the kernel memory statistics.
+
+From: "Godmar Back" <godmar@gmail.com>
+Subject: multiple threads waking up at same clock tick
+To: "Ben Pfaff" <blp@cs.stanford.edu>
+Date: Wed, 1 Mar 2006 08:14:47 -0500
+
+Greg Benson points out another potential TODO item for P1.
+
+----
+One thing I recall:
+
+The alarm tests do not test to see if multiple threads are woken up if
+their timers have expired. That is, students can write a solution
+that just wakes up the first thread on the sleep queue rather than
+check for additional threads. Of course, the next thread will be
+woken up on the next tick. Also, this might be hard to test.
+
+---
+Way to test this: (from Godmar Back)
+
+Thread A with high priority spins until 'ticks' changes, then calls to
+timer_sleep(X), Thread B with lower priority is then resumed, calls
+set_priority to make its priority equal to that of thread A, then
+calls timer_sleep(X), all of that before the next clock interrupt
+arrives.
+
+On wakeup, each thread records wake-up time and calls yield
+immediately, forcing the scheduler to switch to the other
+equal-priority thread. Both wake-up times must be the same (and match
+the planned wake-up time.)
+
+PS:
+I actually tested it and it's hard to pass with the current ips setting.
+The bounds on how quickly a thread would need to be able to return after
+sleep appear too tight. Need another idea.
+
+From: "Godmar Back" <godmar@gmail.com>
+
+For reasons I don't currently understand, some of our students seem
+hesitant to include each thread in a second "all-threads" list and are
+looking for ways to implement the advanced scheduler without one.
+
+Currently, I believe, all tests for the mlfqs are such that all
+threads are either ready or sleeping in timer_sleep(). This allows for
+an incorrect implementation in which recent-cpu and priorities are
+updated only for those threads that are on the alarm list or the ready
+list.
+
+The todo item would be a test where a thread is blocked on a
+semaphore, lock or condition variable and have its recent_cpu decay to
+zero, and check that it's scheduled right after the unlock/up/signal.
+
+From: "Godmar Back" <godmar@gmail.com>
+Subject: set_priority & donation - a TODO item
+To: "Ben Pfaff" <blp@cs.stanford.edu>
+Date: Mon, 20 Feb 2006 22:20:26 -0500
+
+Ben,
+
+it seems that there are currently no tests that check the proper
+behavior of thread_set_priority() when called by a thread that is
+running under priority donation. The proper behavior, I assume, is to
+temporarily drop the donation if the set priority is higher, and to
+reassume the donation should the thread subsequently set its own
+priority again to a level that's lower than a still active donation.
+
+ - Godmar
+
From: Godmar Back <godmar@gmail.com>
Subject: project 4 question/comment regarding caching inode data
To: Ben Pfaff <blp@cs.stanford.edu>
* Finish writing tour.
-* Introduce a "yield" system call to speed up the syn-* tests.
-
via Godmar Back:
-* Project 3 solution needs FS lock.
-
* Get rid of mmap syscall, add sbrk.
-* Make backtrace program accept multiple object file arguments,
- e.g. add -u option to allow backtracing user program also.
-
* page-linear, page-shuffle VM tests do not use enough memory to force
eviction. Should increase memory consumption.
* Add FS persistence test(s).
-* lock_acquire(), lock_release() don't need additional intr_dis/enable
- calls, because the semaphore protects lock->holder.
-
-
-
* process_death test needs improvement
* Internal tests.
. opendir/readdir/closedir
. everything needed for getcwd()
+
+To add partition support:
+
+- Find four partition types that are more or less unused and choose to
+ use them for Pintos. (This is implemented.)
+
+- Bootloader reads partition tables of all BIOS devices to find the
+ first that has the "Pintos kernel" partition type. (This is
+ implemented.) Ideally the bootloader would make sure there is
+ exactly one such partition, but I didn't implement that yet.
+
+- Bootloader reads kernel into memory at 1 MB using BIOS calls. (This
+ is implemented.)
+
+- Kernel arguments have to go into a separate sector because the
+ bootloader is otherwise too big to fit now? (I don't recall if I
+ did anything about this.)
+
+- Kernel at boot also scans partition tables of all the disks it can
+ find to find the ones with the four Pintos partition types (perhaps
+ not all exist). After that, it makes them available to the rest of
+ the kernel (and doesn't allow access to other devices, for safety).
+
+- "pintos" and "pintos-mkdisk" need to write a partition table to the
+ disks that they create. "pintos-mkdisk" will need to take a new
+ parameter specifying the type. (I might have partially implemented
+ this, don't remember.)
+
+- "pintos" should insist on finding a partition header on disks handed
+ to it, for safety.
+
+- Need some way for "pintos" to assemble multiple disks or partitions
+ into a single image that can be copied directly to a USB block
+ device. (I don't know whether I came up with a good solution yet or
+ not, or whether I implemented any of it.)
+
+To add USB support:
+
+- Needs to be able to scan PCI bus for UHCI controller. (I
+ implemented this partially.)
+
+- May want to be able to initialize USB controllers over CardBus
+ bridges. I don't know whether this requires additional work or if
+ it's useful enough to warrant extra work. (It's of special interest
+ for me because I have a laptop that only has USB via CardBus.)
+
+- There are many protocol layers involved: SCSI over USB-Mass Storage
+ over USB over UHCI over PCI. (I may be forgetting one.) I don't
+ know yet whether it's best to separate the layers or to merge (some
+ of) them. I think that a simple and clean organization should be a
+ priority.
+
+- VMware can likely be used for testing because it can expose host USB
+ devices as guest USB devices. This is safer and more convenient
+ than using real hardware for testing.
+
+- Should test with a variety of USB keychain devices because there
+ seems to be wide variation among them, especially in the SCSI
+ protocols they support. Should try to use a "lowest-common
+ denominator" SCSI protocol if any such thing really exists.
+
+- Might want to add a feature whereby kernel arguments can be given
+ interactively, rather than passed on-disk. Needs some though.
projects / pintos-anon / blobdiff