| Message ID | 20210225135700.1381396-2-yury.norov@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arch: enable GENERIC_FIND_FIRST_BIT for MIPS and ARM64 | expand |
On Thu, Feb 25, 2021 at 05:56:59AM -0800, Yury Norov wrote: > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 31bd885b79eb..5596eab04092 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -108,6 +108,7 @@ config ARM64 > select GENERIC_CPU_AUTOPROBE > select GENERIC_CPU_VULNERABILITIES > select GENERIC_EARLY_IOREMAP > + select GENERIC_FIND_FIRST_BIT > select GENERIC_IDLE_POLL_SETUP > select GENERIC_IRQ_IPI > select GENERIC_IRQ_MULTI_HANDLER Acked-by: Will Deacon <will@kernel.org> Catalin can pick this up later in the cycle. Will
On Thu, Feb 25, 2021 at 02:02:06PM +0000, Will Deacon wrote: > On Thu, Feb 25, 2021 at 05:56:59AM -0800, Yury Norov wrote: > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 31bd885b79eb..5596eab04092 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -108,6 +108,7 @@ config ARM64 > > select GENERIC_CPU_AUTOPROBE > > select GENERIC_CPU_VULNERABILITIES > > select GENERIC_EARLY_IOREMAP > > + select GENERIC_FIND_FIRST_BIT > > select GENERIC_IDLE_POLL_SETUP > > select GENERIC_IRQ_IPI > > select GENERIC_IRQ_MULTI_HANDLER > > Acked-by: Will Deacon <will@kernel.org> > > Catalin can pick this up later in the cycle. > > Will Ping?
On Wed, Mar 03, 2021 at 02:17:41PM -0800, Yury Norov wrote: > On Thu, Feb 25, 2021 at 02:02:06PM +0000, Will Deacon wrote: > > On Thu, Feb 25, 2021 at 05:56:59AM -0800, Yury Norov wrote: > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > index 31bd885b79eb..5596eab04092 100644 > > > --- a/arch/arm64/Kconfig > > > +++ b/arch/arm64/Kconfig > > > @@ -108,6 +108,7 @@ config ARM64 > > > select GENERIC_CPU_AUTOPROBE > > > select GENERIC_CPU_VULNERABILITIES > > > select GENERIC_EARLY_IOREMAP > > > + select GENERIC_FIND_FIRST_BIT > > > select GENERIC_IDLE_POLL_SETUP > > > select GENERIC_IRQ_IPI > > > select GENERIC_IRQ_MULTI_HANDLER > > > > Acked-by: Will Deacon <will@kernel.org> > > > > Catalin can pick this up later in the cycle. > > > > Will > > Ping? It's on my list for 5.13 but I'll only start queuing patches after -rc3.
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 31bd885b79eb..5596eab04092 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -108,6 +108,7 @@ config ARM64 select GENERIC_CPU_AUTOPROBE select GENERIC_CPU_VULNERABILITIES select GENERIC_EARLY_IOREMAP + select GENERIC_FIND_FIRST_BIT select GENERIC_IDLE_POLL_SETUP select GENERIC_IRQ_IPI select GENERIC_IRQ_MULTI_HANDLER
ARM64 doesn't implement find_first_{zero}_bit in arch code and doesn't enable it in a config. It leads to using find_next_bit() which is less efficient: 0000000000000000 <find_first_bit>: 0: aa0003e4 mov x4, x0 4: aa0103e0 mov x0, x1 8: b4000181 cbz x1, 38 <find_first_bit+0x38> c: f9400083 ldr x3, [x4] 10: d2800802 mov x2, #0x40 // #64 14: 91002084 add x4, x4, #0x8 18: b40000c3 cbz x3, 30 <find_first_bit+0x30> 1c: 14000008 b 3c <find_first_bit+0x3c> 20: f8408483 ldr x3, [x4], #8 24: 91010045 add x5, x2, #0x40 28: b50000c3 cbnz x3, 40 <find_first_bit+0x40> 2c: aa0503e2 mov x2, x5 30: eb02001f cmp x0, x2 34: 54ffff68 b.hi 20 <find_first_bit+0x20> // b.pmore 38: d65f03c0 ret 3c: d2800002 mov x2, #0x0 // #0 40: dac00063 rbit x3, x3 44: dac01063 clz x3, x3 48: 8b020062 add x2, x3, x2 4c: eb02001f cmp x0, x2 50: 9a829000 csel x0, x0, x2, ls // ls = plast 54: d65f03c0 ret ... 0000000000000118 <_find_next_bit.constprop.1>: 118: eb02007f cmp x3, x2 11c: 540002e2 b.cs 178 <_find_next_bit.constprop.1+0x60> // b.hs, b.nlast 120: d346fc66 lsr x6, x3, #6 124: f8667805 ldr x5, [x0, x6, lsl #3] 128: b4000061 cbz x1, 134 <_find_next_bit.constprop.1+0x1c> 12c: f8667826 ldr x6, [x1, x6, lsl #3] 130: 8a0600a5 and x5, x5, x6 134: ca0400a6 eor x6, x5, x4 138: 92800005 mov x5, #0xffffffffffffffff // #-1 13c: 9ac320a5 lsl x5, x5, x3 140: 927ae463 and x3, x3, #0xffffffffffffffc0 144: ea0600a5 ands x5, x5, x6 148: 54000120 b.eq 16c <_find_next_bit.constprop.1+0x54> // b.none 14c: 1400000e b 184 <_find_next_bit.constprop.1+0x6c> 150: d346fc66 lsr x6, x3, #6 154: f8667805 ldr x5, [x0, x6, lsl #3] 158: b4000061 cbz x1, 164 <_find_next_bit.constprop.1+0x4c> 15c: f8667826 ldr x6, [x1, x6, lsl #3] 160: 8a0600a5 and x5, x5, x6 164: eb05009f cmp x4, x5 168: 540000c1 b.ne 180 <_find_next_bit.constprop.1+0x68> // b.any 16c: 91010063 add x3, x3, #0x40 170: eb03005f cmp x2, x3 174: 54fffee8 b.hi 150 <_find_next_bit.constprop.1+0x38> // b.pmore 178: aa0203e0 mov x0, x2 17c: d65f03c0 ret 180: ca050085 eor x5, x4, x5 184: dac000a5 rbit x5, x5 188: dac010a5 clz x5, x5 18c: 8b0300a3 add x3, x5, x3 190: eb03005f cmp x2, x3 194: 9a839042 csel x2, x2, x3, ls // ls = plast 198: aa0203e0 mov x0, x2 19c: d65f03c0 ret ... 0000000000000238 <find_next_bit>: 238: a9bf7bfd stp x29, x30, [sp, #-16]! 23c: aa0203e3 mov x3, x2 240: d2800004 mov x4, #0x0 // #0 244: aa0103e2 mov x2, x1 248: 910003fd mov x29, sp 24c: d2800001 mov x1, #0x0 // #0 250: 97ffffb2 bl 118 <_find_next_bit.constprop.1> 254: a8c17bfd ldp x29, x30, [sp], #16 258: d65f03c0 ret Enabling find_{first,next}_bit() would also benefit for_each_{set,clear}_bit(). On A-53 find_first_bit() is almost twice faster than find_next_bit(), according to lib/find_bit_benchmark (thanks to Alexey for testing): GENERIC_FIND_FIRST_BIT=n: [7126084.948181] find_first_bit: 47389224 ns, 16357 iterations [7126085.032315] find_first_bit: 19048193 ns, 655 iterations GENERIC_FIND_FIRST_BIT=y: [ 84.158068] find_first_bit: 27193319 ns, 16406 iterations [ 84.233005] find_first_bit: 11082437 ns, 656 iterations GENERIC_FIND_FIRST_BIT=n bloats the kernel despite that it disables generation of find_{first,next}_bit(): yury:linux$ scripts/bloat-o-meter vmlinux vmlinux.ffb add/remove: 4/1 grow/shrink: 19/251 up/down: 564/-1692 (-1128) ... Overall, GENERIC_FIND_FIRST_BIT=n is harmful both in terms of performance and code size, and it's better to have GENERIC_FIND_FIRST_BIT enabled. Tested-by: Alexey Klimov <aklimov@redhat.com> Signed-off-by: Yury Norov <yury.norov@gmail.com> --- arch/arm64/Kconfig | 1 + 1 file changed, 1 insertion(+)