kernel/linux.git/tools/testing/selftests/resctrl/fill_buf.c, branch v6.12.80

selftests/resctrl: Fix memory overflow due to unhandled wraparound

2024-12-05T13:01:33+00:00

[ Upstream commit caf02626b2bf164a02c808240f19dbf97aced664 ] alloc_buffer() allocates and initializes (with random data) a buffer of requested size. The initialization starts from the beginning of the allocated buffer and incrementally assigns sizeof(uint64_t) random data to each cache line. The initialization uses the size of the buffer to control the initialization flow, decrementing the amount of buffer needing to be initialized after each iteration. The size of the buffer is stored in an unsigned (size_t) variable s64 and the test "s64 > 0" is used to decide if initialization is complete. The problem is that decrementing the buffer size may wrap around if the buffer size is not divisible by "CL_SIZE / sizeof(uint64_t)" resulting in the "s64 > 0" test being true and memory beyond the buffer "initialized". Use a signed value for the buffer size to support all buffer sizes. Fixes: a2561b12fe39 ("selftests/resctrl: Add built in benchmark") Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan Signed-off-by: Sasha Levin

selftests/resctrl: Rewrite Cache Allocation Technology (CAT) test

2024-02-13T20:56:45+00:00

CAT test spawns two processes into two different control groups with exclusive schemata. Both the processes alloc a buffer from memory matching their allocated LLC block size and flush the entire buffer out of caches. Since the processes are reading through the buffer only once during the measurement and initially all the buffer was flushed, the test isn't testing CAT. Rewrite the CAT test to allocate a buffer sized to half of LLC. Then perform a sequence of tests with different LLC alloc sizes starting from half of the CBM bits down to 1-bit CBM. Flush the buffer before each test and read the buffer twice. Observe the LLC misses on the second read through the buffer. As the allocated LLC block gets smaller and smaller, the LLC misses will become larger and larger giving a strong signal on CAT working properly. The new CAT test is using only a single process because it relies on measured effect against another run of itself rather than another process adding noise. The rest of the system is set to use the CBM bits not used by the CAT test to keep the test isolated. Replace count_bits() with count_contiguous_bits() to get the first bit position in order to be able to calculate masks based on it. This change has been tested with a number of systems from different generations. Suggested-by: Reinette Chatre Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Read in less obvious order to defeat prefetch optimizations

2024-02-13T20:56:44+00:00

When reading memory in order, HW prefetching optimizations will interfere with measuring how caches and memory are being accessed. This adds noise into the results. Change the fill_buf reading loop to not use an obvious in-order access using multiply by a prime and modulo. Using a prime multiplier with modulo ensures the entire buffer is eventually read. 23 is small enough that the reads are spread out but wrapping does not occur very frequently (wrapping too often can trigger L2 hits more frequently which causes noise to the test because getting the data from LLC is not required). It was discovered that not all primes work equally well and some can cause wildly unstable results (e.g., in an earlier version of this patch, the reads were done in reversed order and 59 was used as the prime resulting in unacceptably high and unstable results in MBA and MBM test on some architectures). Link: https://lore.kernel.org/linux-kselftest/TYAPR01MB6330025B5E6537F94DA49ACB8B499@TYAPR01MB6330.jpnprd01.prod.outlook.com/ Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Replace file write with volatile variable

2024-02-13T20:56:44+00:00

The fill_buf code prevents compiler optimizating the entire read loop away by writing the final value of the variable into a file. While it achieves the goal, writing into a file requires significant amount of work within the innermost test loop and also error handling. A simpler approach is to take advantage of volatile. Writing through a pointer to a volatile variable is enough to prevent compiler from optimizing the write away, and therefore compiler cannot remove the read loop either. Add a volatile 'value_sink' into resctrl_tests.c and make fill_buf to write into it. As a result, the error handling in fill_buf.c can be simplified. Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Refactor fill_buf functions

2024-02-13T20:56:43+00:00

There are unnecessary nested calls in fill_buf.c: - run_fill_buf() calls fill_cache() - alloc_buffer() calls malloc_and_init_memory() Simplify the code flow and remove those unnecessary call levels by moving the called code inside the calling function and remove the duplicated error print. Resolve the difference in run_fill_buf() and fill_cache() parameter name into 'buf_size' which is more descriptive than 'span'. Also, while moving the allocation related code, rename 'p' into 'buf' to be consistent in naming the variables. Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Split fill_buf to allow tests finer-grained control

2024-02-13T20:56:43+00:00

MBM, MBA and CMT test cases call run_fill_buf() that in turn calls fill_cache() to alloc and loop indefinitely around the buffer. This binds buffer allocation and running the benchmark into a single bundle so that a selftest cannot allocate a buffer once and reuse it. CAT test doesn't want to loop around the buffer continuously and after rewrite it needs the ability to allocate the buffer separately. Split buffer allocation out of fill_cache() into alloc_buffer(). This change is part of preparation for the new CAT test that allocates a buffer and does multiple passes over the same buffer (but not in an infinite loop). Co-developed-by: Fenghua Yu Signed-off-by: Fenghua Yu Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Convert perror() to ksft_perror() or ksft_print_msg()

2024-02-13T20:56:43+00:00

The resctrl selftest code contains a number of perror() calls. Some of them come with hash character and some don't. The kselftest framework provides ksft_perror() that is compatible with test output formatting so it should be used instead of adding custom hash signs. Some perror() calls are too far away from anything that sets error. For those call sites, ksft_print_msg() must be used instead. Convert perror() to ksft_perror() or ksft_print_msg(). Other related changes: - Remove hash signs - Remove trailing stops & newlines from ksft_perror() - Add terminating newlines for converted ksft_print_msg() - Use consistent capitalization - Small fixes/tweaks to typos & grammar of the messages - Extract error printing out of PARENT_EXIT() to be able to differentiate Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Don't pass test name to fill_buf

2023-07-25T14:53:48+00:00

Test name is passed to fill_buf functions so that they can loop around buffer only once. This is required for CAT test case. To loop around buffer only once, caller doesn't need to let fill_buf know which test case it is. Instead, pass a boolean argument 'once' which makes fill_buf more generic. As run_benchmark() no longer needs to pass the test name to run_fill_buf(), a few test running functions can be simplified to not write the test name into the default benchmark_cmd. The has_ben argument can also be removed now from those test running functions. Co-developed-by: Fenghua Yu Signed-off-by: Fenghua Yu Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Tested-by: Babu Moger Tested-by: Shaopeng Tan (Fujitsu) Signed-off-by: Shuah Khan

selftests/resctrl: Improve parameter consistency in fill_buf

2023-07-25T14:53:42+00:00

fill_buf's arguments can be improved in multiple ways: - Multiple functions in fill_buf have start_ptr as one of their argument which is a bit long and the extra "start" is pretty obvious when it comes to pointers. - Some of the functions take end_ptr and others size_t to indicate the end of the buffer. - Some arguments meaning buffer size are called just 's' - mem_flush() takes void * but immediately converts it to char * Cleanup the parameters to make things simpler and more consistent: - Rename start_ptr to simply buf as it's shorter. - Replace end_ptr and s parameters with buf_size and only calculate end_ptr in the functions that truly use it. - Make mem_flush() parameters to follow the same convention as the other functions in fill_buf. - convert mem_flush() char * to unsigned char *. While at it, fix also a typo in a comment. Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Tested-by: Babu Moger Tested-by: Shaopeng Tan (Fujitsu) Signed-off-by: Shuah Khan

selftests/resctrl: Remove unnecessary startptr global from fill_buf

2023-07-25T14:53:36+00:00

fill_buf stores buffer pointer into global variable startptr that is only used in fill_cache(). Remove startptr as global variable, the local variable in fill_cache() is enough to keep the pointer. Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre Tested-by: Babu Moger Tested-by: Shaopeng Tan (Fujitsu) Signed-off-by: Shuah Khan