The numeric_forward() function serves as the comparator for qsort() when sorting kernel symbols. For a modern Linux kernel containing hundreds of thousands of symbols (N), qsort() performs O(N log N) comparisons, meaning this function is invoked millions of times during the startup phase of the crash utility. During these millions of comparisons, it frequently checks for specific symbol names (e.g., "_stext", "kaslr_get_random_long") using the STREQ() macro. STREQ() internally expands to string_exists() checks followed by a full strcmp(), incurring significant function call overhead that cannot be optimized out by the compiler at runtime. By explicitly checking the first character of the symbol name (e.g., x->name[0] == '_') before invoking STREQ(), we introduce a lightweight "early reject" mechanism. Since the distribution of kernel symbol starting characters is relatively sparse, this short-circuits the evaluation for the vast majority of symbols, completely avoiding the overhead of strcmp() macro expansion. Additionally, since x->name could potentially be NULL, we must safely guard the character access with an explicit non-null check (x->name &&) to prevent segmentation faults. This O(N log N) cumulative optimization yields a measurable performance improvement in symbol sorting speed, which scales directly with the size of the kernel symbol table. Performance measurement (./crash /proc/kcore startup, n=6 alternating runs on RISC-V 32-core, kernel 6.12.13.bsk.1-rc17-riscv64): before after mean (s) 60.367 48.688 median (s) 58.831 47.588 min (s) 54.980 45.951 max (s) 69.889 52.988 Speedup (mean): 1.24x (-11.68 s, -19.3%) perf stat: instructions: 3.104e11 -> 2.680e11 (-13.7%) cycles: 1.612e11 -> 1.406e11 (-12.8%) perf record (top hotspots): strcmp: 12.59% -> 3.64% string_exists: dropped out of top-10 Signed-off-by: Rui Qi <qirui.001(a)bytedance.com&gt; --- Changes in V2: - Add performance measurement data (time, perf stat, perf record) symbols.c | 40 ++++++++++++++++++++-------------------- 1 file changed, 20 insertions(+), 20 deletions(-) diff --git a/symbols.c b/symbols.c index c0285058c5cb..c0353d626477 100644 --- a/symbols.c +++ b/symbols.c @@ -14412,16 +14412,16 @@ numeric_forward(const void *P_x, const void *P_y) error(FATAL, "bfd_minisymbol_to_symbol failed\n"); if (st->_stext_vmlinux == UNINITIALIZED) { - if (STREQ(x->name, "_stext")) + if (x->name && x->name[0] == '_' && STREQ(x->name, "_stext")) st->_stext_vmlinux = valueof(x); - else if (STREQ(y->name, "_stext")) + else if (y->name && y->name[0] == '_' && STREQ(y->name, "_stext")) st->_stext_vmlinux = valueof(y); } if (kt->flags2 & KASLR_CHECK) { - if (STREQ(x->name, "kaslr_get_random_long") || - STREQ(y->name, "kaslr_get_random_long") || - STREQ(x->name, "module_load_offset") || - STREQ(y->name, "module_load_offset")) { + if ((x->name && x->name[0] == 'k' && STREQ(x->name, "kaslr_get_random_long")) || + (y->name && y->name[0] == 'k' && STREQ(y->name, "kaslr_get_random_long")) || + (x->name && x->name[0] == 'm' && STREQ(x->name, "module_load_offset")) || + (y->name && y->name[0] == 'm' && STREQ(y->name, "module_load_offset"))) { kt->flags2 &= ~KASLR_CHECK; kt->flags2 |= (RELOC_AUTO|KASLR); } @@ -14429,36 +14429,36 @@ numeric_forward(const void *P_x, const void *P_y) if (SADUMP_DUMPFILE() || QEMU_MEM_DUMP_NO_VMCOREINFO() || VMSS_DUMPFILE()) { /* Need for kaslr_offset and phys_base */ - if (STREQ(x->name, "divide_error") || - STREQ(x->name, "asm_exc_divide_error")) + if ((x->name && x->name[0] == 'd' && STREQ(x->name, "divide_error")) || + (x->name && x->name[0] == 'a' && STREQ(x->name, "asm_exc_divide_error"))) st->divide_error_vmlinux = valueof(x); - else if (STREQ(y->name, "divide_error") || - STREQ(y->name, "asm_exc_divide_error")) + else if ((y->name && y->name[0] == 'd' && STREQ(y->name, "divide_error")) || + (y->name && y->name[0] == 'a' && STREQ(y->name, "asm_exc_divide_error"))) st->divide_error_vmlinux = valueof(y); - if (STREQ(x->name, "idt_table")) + if (x->name && x->name[0] == 'i' && STREQ(x->name, "idt_table")) st->idt_table_vmlinux = valueof(x); - else if (STREQ(y->name, "idt_table")) + else if (y->name && y->name[0] == 'i' && STREQ(y->name, "idt_table")) st->idt_table_vmlinux = valueof(y); - if (STREQ(x->name, "kaiser_init")) + if (x->name && x->name[0] == 'k' && STREQ(x->name, "kaiser_init")) st->kaiser_init_vmlinux = valueof(x); - else if (STREQ(y->name, "kaiser_init")) + else if (y->name && y->name[0] == 'k' && STREQ(y->name, "kaiser_init")) st->kaiser_init_vmlinux = valueof(y); - if (STREQ(x->name, "linux_banner")) + if (x->name && x->name[0] == 'l' && STREQ(x->name, "linux_banner")) st->linux_banner_vmlinux = valueof(x); - else if (STREQ(y->name, "linux_banner")) + else if (y->name && y->name[0] == 'l' && STREQ(y->name, "linux_banner")) st->linux_banner_vmlinux = valueof(y); - if (STREQ(x->name, "pti_init")) + if (x->name && x->name[0] == 'p' && STREQ(x->name, "pti_init")) st->pti_init_vmlinux = valueof(x); - else if (STREQ(y->name, "pti_init")) + else if (y->name && y->name[0] == 'p' && STREQ(y->name, "pti_init")) st->pti_init_vmlinux = valueof(y); - if (STREQ(x->name, "saved_command_line")) + if (x->name && x->name[0] == 's' && STREQ(x->name, "saved_command_line")) st->saved_command_line_vmlinux = valueof(x); - else if (STREQ(y->name, "saved_command_line")) + else if (y->name && y->name[0] == 's' && STREQ(y->name, "saved_command_line")) st->saved_command_line_vmlinux = valueof(y); } -- 2.47.3