The __dyndbg_callsite section is basically a flat db-table, an array
of struct _ddebug_callsite[]s. Its data is inherently hierarchical
and sorted, so a field-wise run-length encoding would compress well.
Add counters and code to test 3 fields of consecutive callsites for
repeated values. The results inform a compression estimate.
dyndbg: 2605 entries. repeated entries: 2369 module 2231 file 1147 func
Thats (91%, 86%, 44%) repeated values in those pointers/columns, on my
i7 laptop build. With a zero-overhead markup, like LSB-stealing, we
could mark the differing tails of consecutive records, and get 11/24
compression on init/main pr_debugs.
For a slightly apples-to-oranges comparison (text vs pointers),
`gzip /proc/dynamic_debug/control` achieves 6/1 compression.
Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
---
lib/dynamic_debug.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 2e4a39c349a5..5980d44ff2f8 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1081,11 +1081,12 @@ static int __init dynamic_debug_init_control(void)
static int __init dynamic_debug_init(void)
{
- struct _ddebug *iter, *iter_start;
+ struct _ddebug *iter, *iter_start, *prev = NULL;
const char *modname = NULL;
char *cmdline;
int ret = 0;
int n = 0, entries = 0, modct = 0;
+ int modreps = 0, funcreps = 0, filereps = 0;
if (&__start___dyndbg == &__stop___dyndbg) {
if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) {
@@ -1099,7 +1100,16 @@ static int __init dynamic_debug_init(void)
iter = __start___dyndbg;
modname = iter->site->modname;
iter_start = iter;
- for (; iter < __stop___dyndbg; iter++) {
+ for (prev = iter; iter < __stop___dyndbg; iter++) {
+ if (entries) {
+ if (prev->site->modname == iter->site->modname)
+ modreps++;
+ if (prev->site->function == iter->site->function)
+ funcreps++;
+ if (prev->site->filename == iter->site->filename)
+ filereps++;
+ prev++; /* one behind iter */
+ }
entries++;
if (strcmp(modname, iter->site->modname)) {
modct++;
@@ -1122,6 +1132,9 @@ static int __init dynamic_debug_init(void)
(int)(entries * sizeof(struct _ddebug)),
(int)(entries * sizeof(struct _ddebug_callsite)));
+ vpr_info("%d entries. repeated entries: %d module %d file %d func\n",
+ entries, modreps, filereps, funcreps);
+
/* apply ddebug_query boot param, dont unload tables on err */
if (ddebug_setup_string[0] != '\0') {
pr_warn("ddebug_query param name is deprecated, change it to dyndbg\n");
--
2.28.0
