-*- 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.
+
+- 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: 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.)
+
* Get rid of rox--causes more trouble than it's worth
* Reconsider command line arg style--confuses everyone.
-* pintos script doesn't (always?) delete temp disks
-
* Finish writing tour.
via Godmar Back:
-* Project 3 solution needs FS lock.
-
* Get rid of mmap syscall, add sbrk.
-* hash_destroy() should take function arg.
-
-* Make backtrace program accept multiple object file arguments,
- e.g. add -u option to allow backtracing user program also.
-
-* VM projects do not use enough memory to force eviction.
- Should reduce user limit or increase memory consumption.
-
-
-
+* 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
- 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