[PATCH 17/23] modpost: perform srcversion hashing in parallel
Lorenzo Stoakes (ARM)
ljs at kernel.org
Fri Sep 11 03:49:05 PDT 2026
I'm likely going to be dropping this patch from the series:
https://lore.kernel.org/linux-modules/20260731-module_ver_remove-v2-0-c9163858f382@linuxfoundation.org/
I don't really agree with the points below but not really worth getting into if
the patch is going away :)
On Thu, Sep 10, 2026 at 11:32:59AM +0100, David Laight wrote:
> 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;
> > }
> > -
> > }
> >
> > }
> >
>
--
Cheers, Lorenzo
More information about the linux-riscv
mailing list