-*- text -*-
-* The tests in tests/ don't apply the grading patches.
+Godmar says:
-* We need better and more example programs.
+- 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.
- - Need an mmap example program as a replacement for the crappy mmap FAQ
- question.
+- 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.
- - How about `diff' and `cmp' programs?
+- 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.
-* Make it clear that the students own their code, because there was some
- confusion on that point.
+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
-* Threads:
+here's an idea for future semesters.
- - join-invalid doesn't compile if tid_t is not scalar type.
+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.
- - mlfqs tests suck. They aren't even correct, e.g. the amarv
- submission from win0405 is graded incorrectly.
+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.
-* Userprog project:
+(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.)
- - Don't emphasize that stuff needs to be copied from user space to
- kernel space. Instead, emphasize validation and suggest that
- copying is a common solution and that it will be necessary in
- project 3 and in real OSes. Also revise the grading criteria to
- match.
+* Get rid of rox--causes more trouble than it's worth
- - Move `join' implementation here, from `threads' project, to help
- normalize the project difficulties.
+* Reconsider command line arg style--confuses everyone.
- - The semantics of the join system call should change so that it
- only returns the exit code once.
+* Finish writing tour.
- - 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.
+via Godmar Back:
- - 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.
+* Get rid of mmap syscall, add sbrk.
-* VM project:
+* page-linear, page-shuffle VM tests do not use enough memory to force
+ eviction. Should increase memory consumption.
- - Discuss the perils of mixing dirty bits between kernel and user virtual
- memory.
+* Add FS persistence test(s).
- - Sample solution.
+* process_death test needs improvement
- - Update grading/vm to reflect new mmap, munmap forms.
+* Internal tests.
* Filesys project:
- - Increase maximum disk size from 8 MB to something that actually
- requires doubly indirect nodes. There is a negative pressure here
- from the bitmap object--perhaps we need a specialized bitmap that
- doesn't have to be all in-memory at once.
-
- Alternatively, shrink the inode size.
-
- - Add mkdir and ls example user programs.
-
- - Add option to disable buffer cache.
-
- - Get rid of "dump" commands--they're not really useful.
-
- - Sample solution.
-
- 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.
- - Clarify effect of remove(cwd).
-
* Documentation:
- - Finish writing tour.
-
- Add "Digging Deeper" sections that describe the nitty-gritty x86
details for the benefit of those interested.
- 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()
- - Add src/testcases/vm, src/testcases/filesys and make it clear to use
- them?
+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.
-* Tests:
+- 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.)
- - Release some of them.
+To add USB support:
- - The threads, userprog, vm test source files could use
- factorization and cleanup along the lines of fslib in the filesys
- tests.
+- Needs to be able to scan PCI bus for UHCI controller. (I
+ implemented this partially.)
- - 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.
+- 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.)
-* Code:
+- 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.
- - Rewrite quick_sort() to use heap sort, for O(1) stack usage.
+- 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.
- - Rewrite list_sort() to use merge sort, for O(1) heap usage.
+- 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.
- - Make list_elem and hash_elem a struct, by encapsulating a struct
- list_elem inside a struct hash_elem as a member.
+- 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