CSCI 2122 Assignment 5
Due date: 11:59pm, Tuesday, April 9, 2024, submitted via git
Objectives
The purpose of this assignment is to practice your coding in C, and to reinforce the concepts discussed in
class on pointers, caching, and the memory hierarchy.
In this assignment you will implement a cache simulator that uses a limited amount of memory.
Preparation:
1. Complete Assignment 0 or ensure that the tools you would need to complete it are installed.
2. Clone your assignment repository:
where is your CSID. Please see instructions in Assignment 0 and the tutorials on Brightspace if
you are not sure how.
Inside the repository there is one directory: cachex, where code is to be written. You should set up a
CLion project for this directory. Inside the directory is a tests directory that contains tests that will be
executed each time you submit your code. Please do not modify the tests directory or the .gitlabci.yml file that is found in the root directory. Modifying these files may break the tests. These files will
be replaced with originals when the assignments are graded. You are provided with a sample Makefile
file that can be used to build your program. If you are using CLion, a Makefile will be generated from
the CMakeLists.txt file generated by CLion.
Background:
Fast memory is expensive. Cache designers are limited by the amount of fast memory that they can use.
Furthermore, the fast memory must store not only the data being cached but all the metadata as well,
such as tags, the valid bit, and the timestamp. Naturally, cache designers simulate their designs in software before implementing in hardware. In this assignment, you will do the same.
Your task is to implement a cache module that simulates a cache. The choice of the type of cache is up to
you. Your cache module will be provided with two parameters: F, the amount of “fast” memory that your
cache may use and M, the amount of memory in the simulated system, from which data will be cached.
As well, your module will be provided a pointer to the “fast” memory of size F. Your cache module may
ONLY use this “fast” memory (apart from local variables) to implement the cache. In short, any data that
is needed to manage the cache, as well as the data being cached, must be stored in the “fast” memory.
Caches
Recall that a cache is defined by several parameters:
S: the number of sets
E: the number of lines per set
B: the number of bytes each line caches
The size of the cache is C = S x E x B. The type of cache depends on these parameters:
• In direct mapped caches, E = 1, i.e., there is one (1) line per set,
• In fully associative caches, S = 1, i.e., all lines are in a single set, and
• In set associative caches, S > 1 and E > 1, i.e., there are multiple sets, each with multiple lines.
When a cache receives a memory reference, it
1. Breaks up the address into a tag, a set index, and an offset.
2. Uses the index to identify the set where the referenced memory may be cached
3. Uses the tag to determine if a line in the set is caching the referenced memory
4. If the referenced memory is not being cached,
a. The cache determines if the set contains an unused line
b. If no lines are unused, the cache will evict a used line.
c. The line is then loaded with the block of memory containing the reference.
5. At this point, a line in the selected set is caching the memory being referenced. The cache returns
the data being referenced.
The choice of what type of cache to use, is completely up to you. The only restriction is that all parts of
the cache must fit into F bytes of the “fast” memory and that the line size B ≥ 32 bytes.
Reference Streams
A reference stream is simply a sequence of memory references (addresses), representing a program running and accessing memory as it runs. The first integer, R, denotes
the number of memory references that follow. The next R integers are the memory
addresses.
The Cache Simulator
Your cache simulator takes as input (i) a system configuration that includes:
• F_size: Size of the “fast” memory where F_size ≥ 256
• F_memory: A pointer to the “fast” memory
• M_size: Size of main memory
(ii) a reference stream, and (iii) an optional “stats” command that causes the simulator to print out the
cache hit/miss count and hit-rate. The simulator instantiates the system being simulated and then processes the reference stream, by sending each reference to the cache. The cache will forward the request
to the main memory, if the request causes a miss, loading a line from the memory. Once the requested
data is in the cache, the cache returns the requested data. The simulator counts the hits and misses that
occur, and can output the hit-rate after the reference stream completes.
Your task will be to implement the cache module in the Cache Simulator.
Task: Implement the cache.c for the Simulator
Your task is to implement the cache.c module by implementing one function. The function is declared
in cache.h and is called from main.c. The function is:
int cache_get(unsigned long address, unsigned long *value)
This function takes a memory address and a pointer to a value and loads a word (a long) located
at memory address and copies it into the location pointed to by value. I.e., this is what the CPU
does when it needs to load a word from memory, it requests it from the cache. The function takes
two (2) parameters:
• address : the location of the value to be loaded. Addresses are the memory references
from the reference stream.
• value : a pointer to a buffer of where the word is to be copied into.
The function returns a 1 on success and a 0 on failure. The function performs two steps:
1. Check if the cache system has been initialized. If not, the initialize the cache.
2. Process the request, by returning the value at the specified memory address.
9
22
48
70
4118
22
4118
2070
4118
22
Step 1: Checking and Initializing the Cache
The function has access to a global struct called c_info, which is defined in cache.h. The struct is
struct cache_info {
void *F_memory; /* pointer to "fast" memory */
unsigned int F_size; /* size of "fast" memory (in bytes) */
unsigned int M_size; /* size of main memory (in bytes) */
};
The pointer c_info.F_memory points to a memory chunk of size c_info.F_size. The memory is
initialized to all 0s. This is the only memory, except for local variables that you may use in implementing
the cache. You may not use calloc() or malloc(), or create any additional static or global variables.
The recommended approach is to define a struct and place it at the start of the “fast” memory pointed
to by F_memory. The struct can point to an array of structs representing sets or lines also located in the
“fast” memory. These structs can contain pointers, pointing to lines (that store data), and which are also
kept in the “fast” memory.
Have an “initialized” flag in the struct at the start of the “fast” memory that is set to 1 if the cache is
initialized and 0 otherwise. Hint: create a static init() function in cache.c that is called from
cache_get() if the “initialized” flag is 0. The init() function can then set up all the pointers and
structures. Note: It is up to you to decide on how many sets and lines the cache will have. The only
restrictions are (1) The minimum size of a line (B) must be 32 bytes. And (ii) everything must fit into
F_size bytes of memory. F_size will be greater or equal to 256. Reminder: one of the things that
init()should do is set the initialized flag to 1.
Step 2: Processing a Request
To process a request, the cache_get() function should:
1. Break up the address into a tag, index, and offset.
2. Use the index to locate the correct set.
3. Use the tag to determine if block of memory that includes the address is in one of the lines in
the set.
4. If it is (a cache hit), the offset is used to locate the word in that line, the word should be copied
into the buffer pointed to by value, and then the function returns.
5. Otherwise, it is a cache miss. In this case, a victim line is selected, initialized with the tag of
the needed memory block, and loaded by calling the function
int memget(unsigned int address, void *buffer, unsigned int size)
which is declared in cache.h and defined in main.c. This function takes the address as
the first parameter, a pointer to a buffer where the block should be loaded, and the size of
the block to get. Hint, the buffer should point to the part of the line storing the block. The
function returns 1 on success and 0 on failure. Each call to memget() counts as a miss.
The rest of the cache simulator is already implemented for you! J
The cachex Mainline
The main.c of cachex is already implemented for you. Below is a brief description of what it does.
Input
The cachex reads input from stdin. The input consists of three parts: (i) a system configuration; (ii) a
reference stream; and (iii) an optional “stats” command.
The system configuration consists of two integers:
• F : the “fast” memory size
• M : the memory size
The reference stream consists of an integer N denoting the number of references, followed by N references. Each reference is an integer between 0 and M – 8, denoting the address in memory being referenced.
After the N memory references, and optional “stats” command may be present. This command consists
of a single word “stats” and causes the simulator to print out the hits, misses, and hit-rate.
Processing
When cachex starts running, it reads in the system configuration, allocates the memory in the system
being simulated, and initializes the c_info struct. The main memory is initialized to a sequence of pseudorandom numbers (the numbers look random, but they are not).
It then enters the main loop and processes the reference stream:
• For each reference, cache_get() is called.
• The loaded value is compared to the expected value and any errors are noted.
During the processing, all cache hits and misses are recorded.
If the “stats” command is present after the memory references, the number of hits and misses is displayed.
Output
The cachex outputs to stdout in two parts: (i) the result of each memory reference as it is being processed; (iii) the aggregates of hits and misses, if the stats command was used.
Example
Input Output
1024 65536
9
22
48
70
4118
22
4118
2070
4118
22
stats
Loaded value [0xb9cb17b29e5109d2] @ address 0x00000016
Loaded value [0x0394fee63984c8dc] @ address 0x00000030
Loaded value [0x8eba29a6bb1465ff] @ address 0x00000046
Loaded value [0x3ce65cc676176add] @ address 0x00001016
Loaded value [0xb9cb17b29e5109d2] @ address 0x00000016
Loaded value [0x3ce65cc676176add] @ address 0x00001016
Loaded value [0x425a273223d06058] @ address 0x00000816
Loaded value [0x3ce65cc676176add] @ address 0x00001016
Loaded value [0xb9cb17b29e5109d2] @ address 0x00000016
Cache hits: 4, misses: 5
Hints and Suggestions
• You will need a couple structs, one for cache and one for line. You may also want one for set.
• Fundamentally, a cache is an array of sets, and a set is an array of lines.
• You should only need to modify one file: cache.c.
• There is not a lot of code to write (my solution under 100 lines).
Grading
If your program does not compile, it is considered non-functional and of extremely poor quality, meaning you will receive 0 for the solution.
The assignment will be graded based on three criteria:
Functionality: “Does it work according to specifications?”. This is determined in an automated fashion by
running your program on several inputs and ensuring that the outputs match the expected outputs. The
score is determined based on the number of tests that your program passes. So, if your program passes
t/T tests, you will receive that proportion of the marks.
Performance: “Does it perform well?”. This is determined in an semi-automated fashion by running your
program on several inputs and the comparing benchmarks of your cache to that of the solution.
Quality of Solution: “Is it a good solution?” This considers whether the approach and algorithm in your
solution is correct. This is determined by visual inspection of the code. It is possible to get a good grade
on this part even if you have bugs that cause your code to fail some of the tests.
Code Clarity: “Is it well written?” This considers whether the solution is properly formatted, well documented, and follows coding style guidelines. A single overall mark will be assigned for clarity. Please see
the Style Guide in the Assignment section of the course in Brightspace.
The following grading scheme will be used:
Task 100% 80% 60% 40% 20% 0%
Functionality
(20 marks) Equal to the number of tests passed.
Performance
(10 marks)
Hit rate of cache
meets or exceeds hit rate of
the solution
Hit rate of cache
is ≥80% of the solution
Hit rate of cache
is ≥60% of the solution
Hit rate of cache
is ≥40% of the
solution
Hit rate of
cache is ≥20%
of the solution
code does not compile
No code submitted or
Solution Quality
(10 marks)
Implemented efficiently and correctly.
Implementation is
correct. All three
types of caches
are functional.
Minor flaws with
implementation,
two of three
types of caches
are functional.
Major flaws in
implementation. One of
three types of
caches work.
An attempt
has been
made.
Code Clarity
(10 marks)
Indentation, formatting, naming,
comments
Code looks professional and follows all style
guidelines
Code looks good
and mostly follows style guidelines.
Code is mostly
readable and
mostly follows
some of the style
guidelines
Code is hard to
read and follows few of the
style guidelines
Code is not
legible
Assignment Submission
Submission and testing are done using Git, Gitlab, and Gitlab CI/CD. You can submit as many times as you
wish, up to the deadline. Every time a submission occurs, functional tests are executed, and you can view
the results of the tests. To submit use the same procedure as Assignment 0.
Assignment Testing without Submission
Testing via submission can take some time, especially if the server is loaded. You can run the tests without
submitting your code by using the provided runtests.sh script. Running the script with no arguments
will run all the tests. Running the script with the test number, i.e., 00, 01, 02, 03, … 09, will run that specific
test. Please see below for how run the script.
Get your program ready to run
If you are developing directly on the unix server,
1. SSH into the remote server and be sure you are in the cachex directory.
2. Be sure the program is compiled by running make.
If you are using CLion
1. Run your program on the remote server as described in the CLion tutorials.
2. Open a remote host terminal via Tools → Open Remote Host Terminal
If you are using VSCode
1. Run your program on the remote server as described in VSCode tutorials.
2. Click on the Terminal pane in the bottom half of the window or via Terminal → New Terminal
Run the test script
3. Run the script in the terminal by using the command:
./runtest.sh
to run all the tests, or specify the test number to run a specific test, e.g. :
./runtest.sh 07
Run the benchmark script
3. Run the script in the terminal by using the command:
./runbench.sh
to run all the tests, or specify the test number to run a specific test, e.g. :
./runbench.sh 03
You will see the bench run in the terminal window.
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