[PATCH 17/23] modpost: perform srcversion hashing in parallel
David Laight
david.laight.linux at gmail.com
Thu Sep 10 03:32:59 PDT 2026
On Tue, 08 Sep 2026 21:55:17 +0100
"Lorenzo Stoakes (ARM)" <ljs at kernel.org> wrote:
> modpost does a lot of single-threaded work hashing files from each object's
> .cmd file.
>
> This makes the build slower than it needs to be, so do this work in
> parallel.
>
> This is egregious for allmodconfig builds - for instance x86-64 can end up
> opening 200,000 files individually and hashing them all serially.
>
> Parallelise this operation by maintaining a thread pool for the hashing
> work.
>
> Combined with the per-file hashing commit this cuts modpost's run time
> nearly in half for an allmodconfig build.
>
> Module.symvers and every *.mod.S are byte for byte the same.
>
> modpost is on the serial tail of every allmodconfig build, however
> defconfig does not set CONFIG_MODULE_SRCVERSION_ALL and is unchanged.
>
> Whole build, 128-thread Threadripper 9980X, best of N runs:
>
> before after delta
> -------------------------------
> x86 allmodconfig, touch mm/vma.c, gcc 33.4s 30.2s -3.2s (-10%)
> x86 allmodconfig, touch mm/vma.c, clang 31.1s 28.1s -3.0s (-10%)
>
> Assisted-by: LLM
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs at kernel.org>
> ---
> scripts/mod/Makefile | 1 +
> scripts/mod/modpost.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++--
> scripts/mod/modpost.h | 2 ++
> scripts/mod/sumversion.c | 3 +-
> 4 files changed, 74 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
> index fbd5099e0441..fdd486184f9c 100644
> --- a/scripts/mod/Makefile
> +++ b/scripts/mod/Makefile
> @@ -5,6 +5,7 @@ hostprogs-always-y += modpost mk_elfconfig
> always-y += empty.o
>
> modpost-objs := modpost.o file2alias.o sumversion.o symsearch.o
> +HOSTLDLIBS_modpost := -lpthread
>
> devicetable-offsets-file := devicetable-offsets.h
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 550ccd753ed8..882169e51851 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -16,6 +16,7 @@
> #include <fnmatch.h>
> #include <stdio.h>
> #include <ctype.h>
> +#include <pthread.h>
> #include <string.h>
> #include <limits.h>
> #include <stdbool.h>
> @@ -1717,8 +1718,7 @@ static void read_symbols(const char *modname)
> if (!mod->is_vmlinux) {
> version = get_modinfo(&info, "version");
> if (version || all_versions)
> - get_src_version(mod->name, mod->srcversion,
> - sizeof(mod->srcversion) - 1);
> + mod->need_srcversion = true;
> }
>
> parse_elf_finish(&info);
> @@ -1736,6 +1736,72 @@ static void read_symbols(const char *modname)
> }
> }
>
> +static struct module **srcversion_mods;
> +static unsigned int nr_srcversion_mods, next_srcversion_mod;
> +
> +static bool get_next_src_version(void)
> +{
> + struct module *mod;
> + unsigned int idx;
> +
> + idx = __sync_fetch_and_add(&next_srcversion_mod, 1);
When I've done this is the past, adding 'a few' items was faster
because it reduced the contention on the counter.
(Although there were probably some very cheap 'actions'.)
> + if (idx >= nr_srcversion_mods)
> + return false;
> + mod = srcversion_mods[idx];
> +
> + get_src_version(mod->name, mod->srcversion,
> + sizeof(mod->srcversion) - 1);
> + return true;
> +}
> +
> +static void *srcversion_worker(void *arg)
> +{
> + while (get_next_src_version())
> + ;
I don't think the extra function call helps.
> +
> + return NULL;
> +}
> +
> +static void hash_srcversions(void)
> +{
> + unsigned int i = 0;
> + struct module *mod;
> + pthread_t *threads;
> + long nr_threads;
> +
> + list_for_each_entry(mod, &modules, list)
> + if (mod->need_srcversion)
> + nr_srcversion_mods++;
> +
> + if (!nr_srcversion_mods)
> + return;
> +
> + srcversion_mods = xmalloc(nr_srcversion_mods * sizeof(*srcversion_mods));
> +
> + list_for_each_entry(mod, &modules, list)
> + if (mod->need_srcversion)
> + srcversion_mods[i++] = mod;
> +
> + nr_threads = sysconf(_SC_NPROCESSORS_ONLN);
One thread per cpu is probably a few to many.
It might be worth adding a command line parameter for the 'max threads'.
Possibly with -n meaning 'all but n'.
> + nr_threads = nr_threads < 1 ? 1 : nr_threads; /* On error assume 1. */
> + if (nr_threads > nr_srcversion_mods)
> + nr_threads = nr_srcversion_mods;
> +
> + sumversion_init();
> + threads = xmalloc(nr_threads * sizeof(*threads));
> + for (i = 0; i < nr_threads; i++) {
> + if (pthread_create(&threads[i], NULL, srcversion_worker, NULL)) {
> + perror("pthread_create");
> + exit(1);
> + }
> + }
The main code can call srcversion_worker() here.
David
> + for (i = 0; i < nr_threads; i++)
> + pthread_join(threads[i], NULL);
> +
> + free(threads);
> + free(srcversion_mods);
> +}
> +
> static void read_symbols_from_files(const char *filename)
> {
> FILE *in = stdin;
> @@ -2729,6 +2795,8 @@ int main(int argc, char **argv)
> if (files_source)
> read_symbols_from_files(files_source);
>
> + hash_srcversions();
> +
> list_for_each_entry(mod, &modules, list) {
> keep_no_trim_symbols(mod);
>
> diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
> index d5f6d82837d5..10d5f8f2f293 100644
> --- a/scripts/mod/modpost.h
> +++ b/scripts/mod/modpost.h
> @@ -127,6 +127,7 @@ struct module {
> bool has_init;
> bool has_cleanup;
> char srcversion[25];
> + bool need_srcversion;
> // Missing namespace dependencies
> struct list_head missing_namespaces;
> // Actual imported namespaces
> @@ -213,6 +214,7 @@ void handle_moddevtable(struct module *mod, struct elf_info *info,
> Elf_Sym *sym, const char *symname);
>
> /* sumversion.c */
> +void sumversion_init(void);
> void get_src_version(const char *modname, char sum[], unsigned sumlen);
>
> /* from modpost.c */
> diff --git a/scripts/mod/sumversion.c b/scripts/mod/sumversion.c
> index 5501d6aa0bea..4521b92ef868 100644
> --- a/scripts/mod/sumversion.c
> +++ b/scripts/mod/sumversion.c
> @@ -249,7 +249,7 @@ static int parse_comment(const char *file, unsigned long len)
> /* FIXME: Handle .s files differently (eg. # starts comments) --RR */
> static bool stop_char[256];
>
> -static void sumversion_init(void)
> +void sumversion_init(void)
> {
> static bool done;
> int chr;
> @@ -402,7 +402,6 @@ static int parse_source_files(const char *objfile, struct md4_ctx *md)
> line, strerror(errno));
> goto out_file;
> }
> -
> }
>
> }
>
More information about the linux-riscv
mailing list