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author | Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> | 2023-12-15 17:05:06 +0200 |
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committer | Shuah Khan <skhan@linuxfoundation.org> | 2024-02-13 13:56:44 -0700 |
commit | 90a009db09e2b91990df28e47844d44ae0ef9aa8 (patch) | |
tree | 695150811645bee8178eeb5d3a001b9eccf1f655 /tools/testing/selftests | |
parent | 2892731ec2893252cdbc256a2bd5436b7fd94cf7 (diff) | |
download | linux-stable-90a009db09e2b91990df28e47844d44ae0ef9aa8.tar.gz linux-stable-90a009db09e2b91990df28e47844d44ae0ef9aa8.tar.bz2 linux-stable-90a009db09e2b91990df28e47844d44ae0ef9aa8.zip |
selftests/resctrl: Replace file write with volatile variable
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 <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Diffstat (limited to 'tools/testing/selftests')
-rw-r--r-- | tools/testing/selftests/resctrl/fill_buf.c | 26 | ||||
-rw-r--r-- | tools/testing/selftests/resctrl/resctrl.h | 7 | ||||
-rw-r--r-- | tools/testing/selftests/resctrl/resctrl_tests.c | 4 |
3 files changed, 16 insertions, 21 deletions
diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c index 635f938b11f0..8fe9574db9d8 100644 --- a/tools/testing/selftests/resctrl/fill_buf.c +++ b/tools/testing/selftests/resctrl/fill_buf.c @@ -78,10 +78,9 @@ static void fill_one_span_write(unsigned char *buf, size_t buf_size) } } -static int fill_cache_read(unsigned char *buf, size_t buf_size, bool once) +static void fill_cache_read(unsigned char *buf, size_t buf_size, bool once) { int ret = 0; - FILE *fp; while (1) { ret = fill_one_span_read(buf, buf_size); @@ -90,26 +89,16 @@ static int fill_cache_read(unsigned char *buf, size_t buf_size, bool once) } /* Consume read result so that reading memory is not optimized out. */ - fp = fopen("/dev/null", "w"); - if (!fp) { - ksft_perror("Unable to write to /dev/null"); - return -1; - } - fprintf(fp, "Sum: %d ", ret); - fclose(fp); - - return 0; + *value_sink = ret; } -static int fill_cache_write(unsigned char *buf, size_t buf_size, bool once) +static void fill_cache_write(unsigned char *buf, size_t buf_size, bool once) { while (1) { fill_one_span_write(buf, buf_size); if (once) break; } - - return 0; } static unsigned char *alloc_buffer(size_t buf_size, int memflush) @@ -143,21 +132,16 @@ static unsigned char *alloc_buffer(size_t buf_size, int memflush) int run_fill_buf(size_t buf_size, int memflush, int op, bool once) { unsigned char *buf; - int ret; buf = alloc_buffer(buf_size, memflush); if (!buf) return -1; if (op == 0) - ret = fill_cache_read(buf, buf_size, once); + fill_cache_read(buf, buf_size, once); else - ret = fill_cache_write(buf, buf_size, once); + fill_cache_write(buf, buf_size, once); free(buf); - if (ret) { - printf("\n Error in fill cache\n"); - return -1; - } return 0; } diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h index f22b7897251e..5b9bea505120 100644 --- a/tools/testing/selftests/resctrl/resctrl.h +++ b/tools/testing/selftests/resctrl/resctrl.h @@ -78,6 +78,13 @@ struct perf_event_read { #define CMT_STR "cmt" #define CAT_STR "cat" +/* + * Memory location that consumes values compiler must not optimize away. + * Volatile ensures writes to this location cannot be optimized away by + * compiler. + */ +extern volatile int *value_sink; + extern pid_t bm_pid, ppid; extern char llc_occup_path[1024]; diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c index 2bbe3045a018..f0d573aa363b 100644 --- a/tools/testing/selftests/resctrl/resctrl_tests.c +++ b/tools/testing/selftests/resctrl/resctrl_tests.c @@ -10,6 +10,10 @@ */ #include "resctrl.h" +/* Volatile memory sink to prevent compiler optimizations */ +static volatile int sink_target; +volatile int *value_sink = &sink_target; + static int detect_vendor(void) { FILE *inf = fopen("/proc/cpuinfo", "r"); |