To evaluate optimizations and measure performance regressions across kallsyms lookups, add a lightweight microbenchmark module in lib/. Configure CONFIG_TEST_KALLSYMS_PERF as a built-in test (bool) rather than a loadable module (tristate). Building the test directly into vmlinux allows exercising internal kallsyms traversal APIs without exporting internal symbol iterators (EXPORT_SYMBOL_GPL) to modules, preserving kernel symbol table encapsulation. The module exercises the primary kallsyms resolution paths: 0. Name-to-Address binary search: Benchmarks lookups across common kernel functions (hits) and non-existent symbol strings (misses, exercising the full binary search tree depth). 1. Address-to-Name resolution: Benchmarks address decoding latency via sprint_symbol() and sprint_symbol_no_offset(). 2. Sequential table scan: Measures complete table iteration latency via kallsyms_on_each_symbol(). The module exposes a num_iters parameter (default: 100,000) and a sysfs trigger to repeat benchmark runs on demand. Signed-off-by: Jim Cromie --- Changes in v3: - Convert CONFIG_TEST_KALLSYMS_PERF from tristate to bool and drop kallsyms iterator EXPORT_SYMBOL_GPL exports to preserve security encapsulation (addresses Sashiko AI review). - Drop 'default m' from lib/Kconfig.debug. - Add cond_resched() every 16k iterations to avoid soft lockups. - Replace direct 64-bit division with div_u64() to fix 32-bit builds. - Guard against divide-by-zero when num_iters=0. - Replace tcp_v4_rcv with panic in hit_symbols to prevent failures wo CONFIG_INET. - Switch to late_initcall for built-in invocation. --- lib/Kconfig.debug | 10 ++ lib/Makefile | 1 + lib/test_kallsyms_perf.c | 241 +++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 252 insertions(+) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 134b15a44625..4b9669e64db9 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -3122,6 +3122,16 @@ config TEST_STATIC_KEYS If unsure, say N. +config TEST_KALLSYMS_PERF + bool "kallsyms performance benchmark test module" + depends on KALLSYMS + help + This builds test_kallsyms_perf to benchmark latency across + Name-to-Address binary search, Address-to-Name resolution, + and full table walks. + + If unsure, say N. + config TEST_DYNAMIC_DEBUG tristate "Test DYNAMIC_DEBUG" depends on DYNAMIC_DEBUG diff --git a/lib/Makefile b/lib/Makefile index dfab958327c5..149968ff3f6b 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -85,6 +85,7 @@ obj-$(CONFIG_TEST_RHASHTABLE) += test_rhashtable.o obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_keys.o obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o +obj-$(CONFIG_TEST_KALLSYMS_PERF) += test_kallsyms_perf.o obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy) diff --git a/lib/test_kallsyms_perf.c b/lib/test_kallsyms_perf.c new file mode 100644 index 000000000000..4d0c39c0a94f --- /dev/null +++ b/lib/test_kallsyms_perf.c @@ -0,0 +1,241 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Microbenchmark and correctness test module for kallsyms subsystem + * + * Measures CPU latency across: + * - Name-to-Address binary search (hits & misses) + * - Address-to-Name symbol resolution (sprint_symbol, buildid) + * - Full kernel symbol iteration (kallsyms_on_each_symbol) + */ + +#define pr_fmt(fmt) "test_kallsyms: " fmt + +#include +#include +#include +#include +#include +#include +#include +#include + +static unsigned int num_iters = 100000; +module_param(num_iters, uint, 0644); +MODULE_PARM_DESC(num_iters, "Number of iterations per microbenchmark"); + +static const char * const hit_symbols[] = { + "_printk", + "schedule", + "vfs_read", + "do_sys_openat2", + "kernel_clone", + "panic", + "kallsyms_lookup_names", + "vm_area_alloc", +}; + +static const char * const miss_symbols[] = { + "nonexistent_symbol_0001", + "xyz_dummy_missing_symbol", + "__never_compiled_in_kernel", + "ext4_nonexistent_func_xyz", + "bpf_not_real_helper_stub", + "vfs_missing_handler_probe", + "tcp_v4_unimplemented_path", + "driver_fake_init_routine", +}; + +static int match_cb(void *data, unsigned long addr) +{ + unsigned long *out = data; + + *out = addr; + return 1; +} + +static int count_cb(void *data, const char *name, unsigned long addr) +{ + unsigned long *cnt = data; + + (*cnt)++; + return 0; +} + +static void run_name_lookup_bench(void) +{ + u64 t0, t1, dt_hit, dt_miss; + unsigned long addr = 0; + unsigned int i, nr_hits, nr_misses; + + nr_hits = ARRAY_SIZE(hit_symbols); + nr_misses = ARRAY_SIZE(miss_symbols); + + /* 0. Correctness validation */ + for (i = 0; i < nr_hits; i++) { + const char *sym = hit_symbols[i]; + unsigned long a1 = 0; + + kallsyms_on_each_match_symbol(match_cb, sym, &a1); + if (!a1) + pr_err("CORRECTNESS FAILURE: hit sym '%s' not found\n", sym); + } + for (i = 0; i < nr_misses; i++) { + const char *sym = miss_symbols[i]; + unsigned long a1 = 0; + + kallsyms_on_each_match_symbol(match_cb, sym, &a1); + if (a1) + pr_err("CORRECTNESS FAILURE: miss sym '%s' unexpectedly found a1=%lx\n", + sym, a1); + } + + /* 1. Name search: Existing symbols (Hits) */ + t0 = ktime_get_ns(); + for (i = 0; i < num_iters; i++) { + const char *sym = hit_symbols[i % nr_hits]; + + if (unlikely(!(i & 0x3fff))) + cond_resched(); + + kallsyms_on_each_match_symbol(match_cb, sym, &addr); + OPTIMIZER_HIDE_VAR(addr); + } + t1 = ktime_get_ns(); + dt_hit = t1 - t0; + + /* 2. Name search: Non-existent symbols (Misses - 17 bsearch probes) */ + t0 = ktime_get_ns(); + for (i = 0; i < num_iters; i++) { + const char *sym = miss_symbols[i % nr_misses]; + + if (unlikely(!(i & 0x3fff))) + cond_resched(); + + kallsyms_on_each_match_symbol(match_cb, sym, &addr); + OPTIMIZER_HIDE_VAR(addr); + } + t1 = ktime_get_ns(); + dt_miss = t1 - t0; + + pr_info("Name Search Hit: %llu ns/lookup (%llu ms total, %u iters)\n", + div_u64(dt_hit, num_iters), div_u64(dt_hit, 1000000), num_iters); + pr_info("Name Search Miss: %llu ns/lookup (%llu ms total, %u iters)\n", + div_u64(dt_miss, num_iters), div_u64(dt_miss, 1000000), num_iters); +} + +static void run_address_lookup_bench(void) +{ + u64 t0, t1, dt_sprint, dt_bldid; + char symname[KSYM_SYMBOL_LEN]; + unsigned long addrs[ARRAY_SIZE(hit_symbols)]; + unsigned int i, nr_addrs = 0; + + for (i = 0; i < ARRAY_SIZE(hit_symbols); i++) { + unsigned long addr = 0; + + kallsyms_on_each_match_symbol(match_cb, hit_symbols[i], &addr); + if (addr) + addrs[nr_addrs++] = addr; + } + + if (!nr_addrs) { + pr_warn("Address benchmark skipped: no test addresses resolved\n"); + return; + } + + /* 1. Address-to-name resolution (sprint_symbol) */ + t0 = ktime_get_ns(); + for (i = 0; i < num_iters; i++) { + unsigned long addr = addrs[i % nr_addrs]; + + if (unlikely(!(i & 0x3fff))) + cond_resched(); + + sprint_symbol(symname, addr); + barrier_data(symname); + } + t1 = ktime_get_ns(); + dt_sprint = t1 - t0; + + /* 2. Address without offset (sprint_symbol_no_offset) */ + t0 = ktime_get_ns(); + for (i = 0; i < num_iters; i++) { + unsigned long addr = addrs[i % nr_addrs]; + + if (unlikely(!(i & 0x3fff))) + cond_resched(); + + sprint_symbol_no_offset(symname, addr); + barrier_data(symname); + } + t1 = ktime_get_ns(); + dt_bldid = t1 - t0; + + pr_info("sprint_symbol: %llu ns/lookup (%llu ms total, %u iters)\n", + div_u64(dt_sprint, num_iters), div_u64(dt_sprint, 1000000), num_iters); + pr_info("sprint_symbol_no_offset: %llu ns/lookup (%llu ms total, %u iters)\n", + div_u64(dt_bldid, num_iters), div_u64(dt_bldid, 1000000), num_iters); +} + +static void run_table_walk_bench(void) +{ + u64 t0, t1, dt_walk; + unsigned long total_symbols = 0; + int iter = 50; + int i; + + t0 = ktime_get_ns(); + for (i = 0; i < iter; i++) { + total_symbols = 0; + kallsyms_on_each_symbol(count_cb, &total_symbols); + } + t1 = ktime_get_ns(); + dt_walk = t1 - t0; + + pr_info("Table Full Walk: %llu ns/sym (%llu us/pass, %lu symbols scanned, %d passes)\n", + div_u64(div_u64(dt_walk, iter), total_symbols ? total_symbols : 1), + div_u64(div_u64(dt_walk, iter), 1000), total_symbols, iter); +} + +static int run_kallsyms_benchmark(void) +{ + if (!num_iters) { + pr_err("num_iters must be non-zero\n"); + return -EINVAL; + } + + pr_info("==================================================\n"); + pr_info("Starting kallsyms performance benchmark (iters=%u)\n", num_iters); + pr_info("==================================================\n"); + + run_name_lookup_bench(); + run_address_lookup_bench(); + run_table_walk_bench(); + + pr_info("==================================================\n"); + pr_info("kallsyms benchmark complete\n"); + pr_info("==================================================\n"); + + return 0; +} + +static int param_set_trigger(const char *val, const struct kernel_param *kp) +{ + return run_kallsyms_benchmark(); +} + +static const struct kernel_param_ops param_ops_trigger = { + .set = param_set_trigger, +}; +module_param_cb(run_test, ¶m_ops_trigger, NULL, 0200); +MODULE_PARM_DESC(run_test, "Write 1 to trigger kallsyms benchmark run"); + +static int __init test_kallsyms_init(void) +{ + return run_kallsyms_benchmark(); +} +late_initcall(test_kallsyms_init); + +MODULE_DESCRIPTION("Microbenchmark test module for kallsyms subsystem"); +MODULE_AUTHOR("Jim Cromie "); +MODULE_LICENSE("GPL"); -- 2.55.0