Re: [PATCH 0/5] sched: dynamic: Simplify PREEMPT_DYNAMIC

From: Mark Rutland

Date: Fri Jul 17 2026 - 07:36:09 EST

On Mon, Jul 06, 2026 at 10:00:47AM +0530, Shrikanth Hegde wrote:
> Hi Mark,
>
> On 7/3/26 7:03 PM, Mark Rutland wrote:
> > All architectures which currently suppoort PREEMPT_DYNAMIC select
> > ARCH_HAS_PREEMPT_LAZY. On architectures which select
> > ARCH_HAS_PREEMPT_LAZY, it has not been possible to select the NONE and
> > VOLUNTARY preemption models since v7.0 due to commit:
> >
> > 7dadeaa6e851 ("sched: Further restrict the preemption modes")
> >
> > Hence in practice PREEMPT_DYNAMIC no longer supports the NONE or
> > VOLUNTARY preemption models.
> >
> > This series makes the de-facto situation official by making
> > PREEMPT_DYNAMIC depend on ARCH_HAS_PREEMPT_LAZY, and removing all the
> > redundant code.
>
> This cleanup looks good indeed. little bit more cleanup can be added,
> details of it at the end.
>
> >
> > For x86_64 v7.2-rc1 defconfig built with GCC 10.2.1, this makes the
> > bzImage 28K smaller, mostly due to removing NOPs that will never be
> > patched to {cond,might}_resched() at runtime:
> >
> > [mark@lakrids:~/src/linux]% ls -al vmlinux-*
> > -rwxr-xr-x 1 mark mark 53844952 Jul 3 14:09 vmlinux-after
> > -rwxr-xr-x 1 mark mark 53842856 Jul 3 14:09 vmlinux-before
>
> Is this reversed? How come vmlinux is more whereas bzImage is less?

Not reversed! The vmlinux after is bigger (but the bzImage is smaller).
I'm not immediately sure why.

I rebuilt afresh, and I see:

[mark@lakrids:~/src/linux]% ls -l ../vmlinux-*
-rwxr-xr-x 1 mark mark 53844952 Jul 6 15:42 ../vmlinux-after
-rwxr-xr-x 1 mark mark 53842856 Jul 6 15:45 ../vmlinux-before
[mark@lakrids:~/src/linux]% size ../vmlinux-*
text data bss dec hex filename
31064917 8823782 1112412 41001111 271a097 ../vmlinux-after
31066343 8860886 1112548 41039777 27237a1 ../vmlinux-before
[mark@lakrids:~/src/linux]% readelf -S ../vmlinux-*

File: ../vmlinux-after
There are 47 section headers, starting at offset 0x3359018:

Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .text PROGBITS ffffffff81000000 00200000
00000000012a5588 0000000000000000 AX 0 0 4096
[ 2] .rodata PROGBITS ffffffff82400000 01600000
0000000000757ae6 0000000000000000 WA 0 0 4096
[ 3] .pci_fixup PROGBITS ffffffff82b57af0 01d57af0
0000000000003c60 0000000000000000 A 0 0 16
[ 4] .tracedata PROGBITS ffffffff82b5b750 01d5b750
0000000000000078 0000000000000000 A 0 0 1
[ 5] __ksymtab PROGBITS ffffffff82b5b7c8 01d5b7c8
0000000000025fec 0000000000000000 A 0 0 4
[ 6] __kflagstab PROGBITS ffffffff82b817b4 01d817b4
00000000000032a9 0000000000000000 A 0 0 1
[ 7] __ksymtab_strings PROGBITS ffffffff82b84a5d 01d84a5d
00000000000412a9 0000000000000001 AMS 0 0 1
[ 8] __init_rodata PROGBITS ffffffff82bc5d20 01dc5d20
0000000000000030 0000000000000000 A 0 0 32
[ 9] __param PROGBITS ffffffff82bc5d50 01dc5d50
00000000000056e0 0000000000000000 A 0 0 8
[10] __modver PROGBITS ffffffff82bcb430 01dcb430
00000000000003f0 0000000000000000 A 0 0 8
[11] __ex_table PROGBITS ffffffff82bcb820 01dcb820
00000000000046b0 000000000000000c AM 0 0 4
[12] .notes NOTE ffffffff82bcfed0 01dcfed0
0000000000000054 0000000000000000 A 0 0 4
[13] .data PROGBITS ffffffff82c00000 01e00000
00000000002edf80 0000000000000000 WAX 0 0 8192
[14] __bug_table PROGBITS ffffffff82eedf80 020edf80
000000000002f4e0 0000000000000000 WA 0 0 1
[15] .orc_header PROGBITS ffffffff82f1d460 0211d460
0000000000000014 0000000000000000 A 0 0 4
[16] .orc_unwind_ip PROGBITS ffffffff82f1d474 0211d474
0000000000233238 0000000000000000 A 0 0 1
[17] .orc_unwind PROGBITS ffffffff831506ac 023506ac
000000000034cb54 0000000000000000 A 0 0 1
[18] .orc_lookup NOBITS ffffffff8349d200 0269d200
000000000004a95c 0000000000000000 WA 0 0 1
[19] .init.text PROGBITS ffffffff834e8000 026e8000
000000000008e59f 0000000000000000 AX 0 0 16
[20] .altinstr_aux PROGBITS ffffffff8357659f 0277659f
0000000000003a61 0000000000000000 AX 0 0 1
[21] .init.data PROGBITS ffffffff8357a000 0277a000
00000000000b75b0 0000000000000000 WA 0 0 8192
[22] .x86_cpu_dev.init PROGBITS ffffffff836315b0 028315b0
0000000000000028 0000000000000000 A 0 0 8
[23] .retpoline_sites PROGBITS ffffffff836315d8 028315d8
0000000000011084 0000000000000000 A 0 0 1
[24] .return_sites PROGBITS ffffffff83642660 02842660
0000000000048f60 0000000000000000 A 0 0 1
[25] .call_sites PROGBITS ffffffff8368b5c0 0288b5c0
00000000000fb5b4 0000000000000000 A 0 0 1
[26] .ibt_endbr_seal PROGBITS ffffffff83786b78 02986b78
000000000000f160 0000000000000000 A 0 0 1
[27] .altinstructions PROGBITS ffffffff83795cd8 02995cd8
0000000000009fe8 000000000000000e AM 0 0 1
[28] .altinstr_re[...] PROGBITS ffffffff8379fcc0 0299fcc0
0000000000002720 0000000000000000 AX 0 0 1
[29] .apicdrivers PROGBITS ffffffff837a23e0 029a23e0
0000000000000018 0000000000000000 WA 0 0 8
[30] .exit.text PROGBITS ffffffff837a2400 029a2400
0000000000003b8b 0000000000000000 AX 0 0 16
[31] .data..percpu PROGBITS ffffffff837a6000 029a6000
000000000002ae58 0000000000000000 WA 0 0 4096
[32] runtime_shif[...] PROGBITS ffffffff837d0e58 029d0e58
0000000000000014 0000000000000000 A 0 0 1
[33] runtime_ptr_[...] PROGBITS ffffffff837d0e70 029d0e70
0000000000000014 0000000000000000 A 0 0 1
[34] runtime_ptr_[...] PROGBITS ffffffff837d0e88 029d0e88
0000000000000014 0000000000000000 A 0 0 1
[35] runtime_ptr_[...] PROGBITS ffffffff837d0ea0 029d0ea0
0000000000000014 0000000000000000 A 0 0 1
[36] runtime_ptr_[...] PROGBITS ffffffff837d0eb8 029d0eb8
0000000000000010 0000000000000000 A 0 0 1
[37] runtime_ptr_[...] PROGBITS ffffffff837d0ec8 029d0ec8
000000000000000c 0000000000000000 A 0 0 1
[38] runtime_ptr_[...] PROGBITS ffffffff837d0ed8 029d0ed8
0000000000000274 0000000000000000 A 0 0 1
[39] .smp_locks PROGBITS ffffffff837d2000 029d2000
000000000000e000 0000000000000000 A 0 0 4
[40] .data_nosave PROGBITS ffffffff837e0000 029e0000
0000000000001000 0000000000000000 WA 0 0 4
[41] .bss NOBITS ffffffff837e1000 029e1000
0000000000095000 0000000000000000 WA 0 0 4096
[42] .brk NOBITS ffffffff83876000 029e1000
0000000000030000 0000000000000000 WA 0 0 1
[43] .comment PROGBITS 0000000000000000 029e1000
0000000000000027 0000000000000001 MS 0 0 1
[44] .symtab SYMTAB 0000000000000000 029e1028
0000000000550530 0000000000000018 45 157665 8
[45] .strtab STRTAB 0000000000000000 02f31558
000000000042784a 0000000000000000 0 0 1
[46] .shstrtab STRTAB 0000000000000000 03358da2
0000000000000273 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
l (large), p (processor specific)

File: ../vmlinux-before
There are 47 section headers, starting at offset 0x33587e8:

Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .text PROGBITS ffffffff81000000 00200000
00000000012a7770 0000000000000000 AX 0 0 4096
[ 2] .rodata PROGBITS ffffffff82400000 01600000
0000000000760c46 0000000000000000 WA 0 0 4096
[ 3] .pci_fixup PROGBITS ffffffff82b60c50 01d60c50
0000000000003c60 0000000000000000 A 0 0 16
[ 4] .tracedata PROGBITS ffffffff82b648b0 01d648b0
0000000000000078 0000000000000000 A 0 0 1
[ 5] __ksymtab PROGBITS ffffffff82b64928 01d64928
0000000000026028 0000000000000000 A 0 0 4
[ 6] __kflagstab PROGBITS ffffffff82b8a950 01d8a950
00000000000032ae 0000000000000000 A 0 0 1
[ 7] __ksymtab_strings PROGBITS ffffffff82b8dbfe 01d8dbfe
00000000000412e0 0000000000000001 AMS 0 0 1
[ 8] __init_rodata PROGBITS ffffffff82bceee0 01dceee0
0000000000000030 0000000000000000 A 0 0 32
[ 9] __param PROGBITS ffffffff82bcef10 01dcef10
00000000000056e0 0000000000000000 A 0 0 8
[10] __modver PROGBITS ffffffff82bd45f0 01dd45f0
00000000000003f0 0000000000000000 A 0 0 8
[11] __ex_table PROGBITS ffffffff82bd49e0 01dd49e0
00000000000046b0 000000000000000c AM 0 0 4
[12] .notes NOTE ffffffff82bd9090 01dd9090
0000000000000054 0000000000000000 A 0 0 4
[13] .data PROGBITS ffffffff82c00000 01e00000
00000000002edf80 0000000000000000 WAX 0 0 8192
[14] __bug_table PROGBITS ffffffff82eedf80 020edf80
000000000002f470 0000000000000000 WA 0 0 1
[15] .orc_header PROGBITS ffffffff82f1d3f0 0211d3f0
0000000000000014 0000000000000000 A 0 0 4
[16] .orc_unwind_ip PROGBITS ffffffff82f1d404 0211d404
00000000002339d4 0000000000000000 A 0 0 1
[17] .orc_unwind PROGBITS ffffffff83150dd8 02350dd8
000000000034d6be 0000000000000000 A 0 0 1
[18] .orc_lookup NOBITS ffffffff8349e498 0269e496
000000000004a9e4 0000000000000000 WA 0 0 1
[19] .init.text PROGBITS ffffffff834e9000 026e9000
000000000008e53f 0000000000000000 AX 0 0 16
[20] .altinstr_aux PROGBITS ffffffff8357753f 0277753f
0000000000003ac1 0000000000000000 AX 0 0 1
[21] .init.data PROGBITS ffffffff8357c000 0277c000
00000000000b75b0 0000000000000000 WA 0 0 8192
[22] .x86_cpu_dev.init PROGBITS ffffffff836335b0 028335b0
0000000000000028 0000000000000000 A 0 0 8
[23] .retpoline_sites PROGBITS ffffffff836335d8 028335d8
0000000000011064 0000000000000000 A 0 0 1
[24] .return_sites PROGBITS ffffffff83644640 02844640
0000000000048f28 0000000000000000 A 0 0 1
[25] .call_sites PROGBITS ffffffff8368d568 0288d568
00000000000f863c 0000000000000000 A 0 0 1
[26] .ibt_endbr_seal PROGBITS ffffffff83785ba8 02985ba8
000000000000f15c 0000000000000000 A 0 0 1
[27] .altinstructions PROGBITS ffffffff83794d08 02994d08
0000000000009fe8 000000000000000e AM 0 0 1
[28] .altinstr_re[...] PROGBITS ffffffff8379ecf0 0299ecf0
0000000000002720 0000000000000000 AX 0 0 1
[29] .apicdrivers PROGBITS ffffffff837a1410 029a1410
0000000000000018 0000000000000000 WA 0 0 8
[30] .exit.text PROGBITS ffffffff837a1430 029a1430
0000000000003b8b 0000000000000000 AX 0 0 16
[31] .data..percpu PROGBITS ffffffff837a5000 029a5000
000000000002ae58 0000000000000000 WA 0 0 4096
[32] runtime_shif[...] PROGBITS ffffffff837cfe58 029cfe58
0000000000000014 0000000000000000 A 0 0 1
[33] runtime_ptr_[...] PROGBITS ffffffff837cfe70 029cfe70
0000000000000014 0000000000000000 A 0 0 1
[34] runtime_ptr_[...] PROGBITS ffffffff837cfe88 029cfe88
0000000000000014 0000000000000000 A 0 0 1
[35] runtime_ptr_[...] PROGBITS ffffffff837cfea0 029cfea0
0000000000000014 0000000000000000 A 0 0 1
[36] runtime_ptr_[...] PROGBITS ffffffff837cfeb8 029cfeb8
0000000000000010 0000000000000000 A 0 0 1
[37] runtime_ptr_[...] PROGBITS ffffffff837cfec8 029cfec8
000000000000000c 0000000000000000 A 0 0 1
[38] runtime_ptr_[...] PROGBITS ffffffff837cfed8 029cfed8
0000000000000274 0000000000000000 A 0 0 1
[39] .smp_locks PROGBITS ffffffff837d1000 029d1000
000000000000e000 0000000000000000 A 0 0 4
[40] .data_nosave PROGBITS ffffffff837df000 029df000
0000000000001000 0000000000000000 WA 0 0 4
[41] .bss NOBITS ffffffff837e0000 029e0000
0000000000095000 0000000000000000 WA 0 0 4096
[42] .brk NOBITS ffffffff83875000 029e0000
0000000000030000 0000000000000000 WA 0 0 1
[43] .comment PROGBITS 0000000000000000 029e0000
0000000000000027 0000000000000001 MS 0 0 1
[44] .symtab SYMTAB 0000000000000000 029e0028
0000000000550830 0000000000000018 45 157685 8
[45] .strtab STRTAB 0000000000000000 02f30858
0000000000427d16 0000000000000000 0 0 1
[46] .shstrtab STRTAB 0000000000000000 0335856e
0000000000000273 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
l (large), p (processor specific)

> Btw, I ran it on powerpc, builds and boots.

Thanks for testing!

> Bloat-o-meter says,
> Total: Before=32286154, After=32267870, chg -0.06%

Yep, similar on x86_64, v7.21-r1, defconfig:

Total: Before=24064357, After=24052508, chg -0.05%

Similar on arm64 too, but I don't have the numbers to hand.

[...]

> In addition,
> I think you can also remove accessor methods of none, voluntary.
> I see preempt_model_none is used. (Though one may question its usage there).
> That wrapper can be outside of #ifdef as preempt dynamic can't choose
> none/voluntary.

Sure.

For consistency, I think it makes sense to keep implementations of
preempt_model_none() and preempt_model_voluntary() that just check
CONFIG_PREEMPT_{NONE,VOLUNTARY}, as in your diff below, even if we only
use preempt_model_none() in one place today.

I'll add a patch to the end of the series.

Thanks!

Mark.

>
> ---
>
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index d964f965c8ff..b4dd4fc13cf8 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -469,22 +469,9 @@ DEFINE_LOCK_GUARD_0(preempt, preempt_disable(), preempt_enable())
> DEFINE_LOCK_GUARD_0(preempt_notrace, preempt_disable_notrace(), preempt_enable_notrace())
> #ifdef CONFIG_PREEMPT_DYNAMIC
> -
> -extern bool preempt_model_none(void);
> -extern bool preempt_model_voluntary(void);
> extern bool preempt_model_full(void);
> extern bool preempt_model_lazy(void);
> -
> #else
> -
> -static inline bool preempt_model_none(void)
> -{
> - return IS_ENABLED(CONFIG_PREEMPT_NONE);
> -}
> -static inline bool preempt_model_voluntary(void)
> -{
> - return IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY);
> -}
> static inline bool preempt_model_full(void)
> {
> return IS_ENABLED(CONFIG_PREEMPT);
> @@ -494,9 +481,16 @@ static inline bool preempt_model_lazy(void)
> {
> return IS_ENABLED(CONFIG_PREEMPT_LAZY);
> }
> -
> #endif
> +static inline bool preempt_model_none(void)
> +{
> + return IS_ENABLED(CONFIG_PREEMPT_NONE);
> +}
> +static inline bool preempt_model_voluntary(void)
> +{
> + return IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY);
> +}
> static inline bool preempt_model_rt(void)
> {
> return IS_ENABLED(CONFIG_PREEMPT_RT);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9eb279eade26..59a8c8e63ca1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7815,8 +7815,6 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write);
> enum {
> preempt_dynamic_undefined = -1,
> - preempt_dynamic_none,
> - preempt_dynamic_voluntary,
> preempt_dynamic_full,
> preempt_dynamic_lazy,
> };
> @@ -7901,8 +7899,6 @@ static void __init preempt_dynamic_init(void)
> } \
> EXPORT_SYMBOL_GPL(preempt_model_##mode)
> -PREEMPT_MODEL_ACCESSOR(none);
> -PREEMPT_MODEL_ACCESSOR(voluntary);
> PREEMPT_MODEL_ACCESSOR(full);
> PREEMPT_MODEL_ACCESSOR(lazy);
>