On Fri, Sep 30, 2022 at 12:27:12PM +0200, Rasmus Villemoes wrote: > Currently, slab_sysfs_init() is an __initcall aka device_initcall. It > is rather time-consuming; on my board it takes around 11ms. That's > about 1% of the time budget I have from U-Boot letting go and until > linux must assume responsibility of keeping the external watchdog > happy. > > There's no particular reason this would need to run at device_initcall > time, so instead make it a late_initcall to allow vital functionality > to get started a bit sooner. > > This actually ends up winning more than just those 11ms, because the > slab caches that get created during other device_initcalls (and before > my watchdog device gets probed) now don't end up doing the somewhat > expensive sysfs_slab_add() themselves. Some example lines (with > initcall_debug set) before/after: > > initcall ext4_init_fs+0x0/0x1ac returned 0 after 1386 usecs > initcall journal_init+0x0/0x138 returned 0 after 517 usecs > initcall init_fat_fs+0x0/0x68 returned 0 after 294 usecs > > initcall ext4_init_fs+0x0/0x1ac returned 0 after 240 usecs > initcall journal_init+0x0/0x138 returned 0 after 32 usecs > initcall init_fat_fs+0x0/0x68 returned 0 after 18 usecs > > Altogether, this means I now get to petting the watchdog around 17ms > sooner. [Of course, the time the other initcalls save is instead spent > in slab_sysfs_init(), which goes from 11ms to 16ms, so there's no > overall change in boot time.] This looks okay and just curious, can you explain what kind of benefit does enabling watchdog early provides? > Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> > --- > > The numbers certainly suggest that someone might want to look into > making sysfs/kobject/kset perform better. But that would be way more > complicated than this patch, and could not possibly achieve the same > win as getting the sysfs_slab_add() overhead completely out of the > way. > > > mm/slub.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 4b98dff9be8e..dade5c84a7bb 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6070,8 +6070,7 @@ static int __init slab_sysfs_init(void) > mutex_unlock(&slab_mutex); > return 0; > } > - > -__initcall(slab_sysfs_init); > +late_initcall(slab_sysfs_init); > #endif /* CONFIG_SYSFS */ > > #if defined(CONFIG_SLUB_DEBUG) && defined(CONFIG_DEBUG_FS) > -- > 2.37.2 This is only deferring slub's sysfs initialization step (still before init process) So IIUC it shouldn't be serious. -- Thanks, Hyeonggon
