-*- text -*-
-* The p1-4.c testcase needs significant tuning. Currently it takes
- too long (especially when SHOW_PROGRESS is turned on) and doesn't
- show significant improvement.
+Godmar says:
-* The semantics of the join system call should change so that it only
- returns the exit code once.
+- 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.
-* mmap/munmap should use segment IDs like Nachos. Too hard otherwise.
+- 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.)
-* Finish writing the tour.
+- 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.
-* Come up with a way for us to release some of the tests.
+- 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.
-* userprog project should mark read-only pages as actually read-only
- in the page table
+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
-* Add src/testcases/vm, src/testcases/filesys and make it clear to use
- them?
+Ben,
-* Speed up disk routines: filling an 8 MB disk takes a long time.
- (They're only slow because timer_sleep always waits for at least one
- timer tick.)
+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: on caching in project 4
+To: Ben Pfaff <blp@cs.stanford.edu>
+Date: Mon, 9 Jan 2006 20:58:01 -0500
+
+here's an idea for future semesters.
+
+I'm in the middle of project 4, I've started by implementing a buffer
+cache and plugging it into the existing filesystem. Along the way I
+was wondering how we could test the cache.
+
+Maybe one could adopt a similar testing strategy as in project 1 for
+the MLQFS scheduler: add a function that reads "get_cache_accesses()"
+and a function "get_cache_hits()". Then create a version of pintos
+that creates access traces for a to-be-determined workload. Run an
+off-line analysis that would determine how many hits a perfect cache
+would have (MAX), and how much say an LRU strategy would give (MIN).
+Then add a fudge factor to account for different index strategies and
+test that the reported number of cache hits/accesses is within (MIN,
+MAX) +/- fudge factor.
+
+(As an aside - I am curious why you chose to use a clock-style
+algorithm rather than the more straightforward LRU for your buffer
+cache implementation in your sample solution. Is there a reason for
+that? I was curious to see if it made a difference, so I implemented
+LRU for your cache implementation and ran the test workload of project
+4 and printed cache hits/accesses.
+I found that for that workload, the clock-based algorithm performs
+almost identical to LRU (within about 1%, but I ran nondeterministally
+with QEMU). I then reduced the cache size to 32 blocks and found again
+the same performance, which raises the suspicion that the test
+workload might not force any cache replacement, so the eviction
+strategy doesn't matter.)
+
+Godmar Back <godmar@gmail.com> writes:
+
+> in your sample solution to P4, dir_reopen does not take any locks when
+> changing a directory's open_cnt. This looks like a race condition to
+> me, considering that dir_reopen is called from execute_process without
+> any filesystem locks held.
+
+* Get rid of rox--causes more trouble than it's worth
+
+* Reconsider command line arg style--confuses everyone.
+
+* Finish writing tour.
+
+via Godmar Back:
+
+* Get rid of mmap syscall, add sbrk.
+
+* page-linear, page-shuffle VM tests do not use enough memory to force
+ eviction. Should increase memory consumption.
+
+* Add FS persistence test(s).
+
+* process_death test needs improvement
+
+* Internal tests.
+
+* Improve automatic interpretation of exception messages.
+
+* Userprog project:
+
+ - Mark read-only pages as actually read-only in the page table. Or,
+ since this was consistently rated as the easiest project by the
+ students, require them to do it.
+
+ - Don't provide per-process pagedir implementation but only
+ single-process implementation and require students to implement
+ the separation? This project was rated as the easiest after all.
+ Alternately we could just remove the synchronization on pid
+ selection and check that students fix it.
+
+* Filesys project:
+
+ - Need a better way to measure performance improvement of buffer
+ cache. Some students reported that their system was slower with
+ cache--likely, Bochs doesn't simulate a disk with a realistic
+ speed.
+
+* Documentation:
+
+ - Add "Digging Deeper" sections that describe the nitty-gritty x86
+ details for the benefit of those interested.
+
+ - Add explanations of what "real" OSes do to give students some
+ perspective.
+
+* Assignments:
+
+ - Add extra credit:
+
+ . Low-level x86 stuff, like paged page tables.
+
+ . Specifics on how to implement sbrk, malloc.
+
+ . Other good ideas.
+
+ . 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