tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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Merge tag 'ftrace-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ftrace update from Steven Rostedt:

- Speed up ftrace_lookup_symbols() for single lookups

The kallsyms lookup in ftrace_lookup_symbols() does a linear search
over each symbol. This is fine when it must match multiple strings,
but when there's only a single string being searched for, using a
binary search is much more efficient. When a single string is passed
in to search, use the binary search method.

* tag 'ftrace-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
ftrace: Use kallsyms binary search for single-symbol lookup

Linus Torvalds 15218296 aec2f682

+22
+22
kernel/trace/ftrace.c
··· 9267 9267 * @addrs array, which needs to be big enough to store at least @cnt 9268 9268 * addresses. 9269 9269 * 9270 + * For a single symbol (cnt == 1), uses kallsyms_lookup_name() which 9271 + * performs an O(log N) binary search via the sorted kallsyms index. 9272 + * This avoids the full O(N) linear scan over all kernel symbols that 9273 + * the multi-symbol path requires. 9274 + * 9275 + * For multiple symbols, uses a single-pass linear scan via 9276 + * kallsyms_on_each_symbol() with binary search into the sorted input 9277 + * array. 9278 + * 9270 9279 * Returns: 0 if all provided symbols are found, -ESRCH otherwise. 9271 9280 */ 9272 9281 int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs) ··· 9283 9274 struct kallsyms_data args; 9284 9275 int found_all; 9285 9276 9277 + /* Fast path: single symbol uses O(log N) binary search */ 9278 + if (cnt == 1) { 9279 + addrs[0] = kallsyms_lookup_name(sorted_syms[0]); 9280 + if (addrs[0] && ftrace_location(addrs[0])) 9281 + return 0; 9282 + /* 9283 + * Binary lookup can fail for duplicate symbol names 9284 + * where the first match is not ftrace-instrumented. 9285 + * Retry with linear scan. 9286 + */ 9287 + } 9288 + 9289 + /* Batch path: single-pass O(N) linear scan */ 9286 9290 memset(addrs, 0, sizeof(*addrs) * cnt); 9287 9291 args.addrs = addrs; 9288 9292 args.syms = sorted_syms;