| Message ID | 20230221190916.572454-7-ajones@ventanamicro.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v5,1/8] RISC-V: alternatives: Support patching multiple insns in assembly | expand |
On 21/02/2023 19:09, Andrew Jones wrote: > Using memset() to zero a 4K page takes 563 total instructions, where > 20 are branches. clear_page(), with Zicboz and a 64 byte block size, > takes 169 total instructions, where 4 are branches and 33 are nops. > Even though the block size is a variable, thanks to alternatives, we > can still implement a Duff device without having to do any preliminary > calculations. This is achieved by using the alternatives' cpufeature > value (the upper 16 bits of patch_id). The value used is the maximum > zicboz block size order accepted at the patch site. This enables us > to stop patching / unrolling when 4K bytes have been zeroed (we would > loop and continue after 4K if the page size would be larger) > > For 4K pages, unrolling 16 times allows block sizes of 64 and 128 to > only loop a few times and larger block sizes to not loop at all. Since > cbo.zero doesn't take an offset, we also need an 'add' after each > instruction, making the loop body 112 to 160 bytes. Hopefully this > is small enough to not cause icache misses. > > Signed-off-by: Andrew Jones <ajones@ventanamicro.com> > Acked-by: Conor Dooley <conor.dooley@microchip.com> > --- > arch/riscv/Kconfig | 13 ++++++ > arch/riscv/include/asm/insn-def.h | 4 ++ > arch/riscv/include/asm/page.h | 6 ++- > arch/riscv/kernel/cpufeature.c | 11 +++++ > arch/riscv/lib/Makefile | 1 + > arch/riscv/lib/clear_page.S | 73 +++++++++++++++++++++++++++++++ > 6 files changed, 107 insertions(+), 1 deletion(-) > create mode 100644 arch/riscv/lib/clear_page.S [snip] > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c > index 0594989ead63..4a496552b812 100644 > --- a/arch/riscv/kernel/cpufeature.c > +++ b/arch/riscv/kernel/cpufeature.c > @@ -292,6 +292,17 @@ static bool riscv_cpufeature_patch_check(u16 id, u16 value) > if (!value) > return true; > > + switch (id) { > + case RISCV_ISA_EXT_ZICBOZ: > + /* > + * Zicboz alternative applications provide the maximum > + * supported block size order, or zero when it doesn't > + * matter. If the current block size exceeds the maximum, > + * then the alternative cannot be applied. > + */ > + return riscv_cboz_block_size <= (1U << value); > + } > + > return false; > } > > diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile > index 6c74b0bedd60..26cb2502ecf8 100644 > --- a/arch/riscv/lib/Makefile > +++ b/arch/riscv/lib/Makefile > @@ -8,5 +8,6 @@ lib-y += strlen.o > lib-y += strncmp.o > lib-$(CONFIG_MMU) += uaccess.o > lib-$(CONFIG_64BIT) += tishift.o > +lib-$(CONFIG_RISCV_ISA_ZICBOZ) += clear_page.o > > obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o > diff --git a/arch/riscv/lib/clear_page.S b/arch/riscv/lib/clear_page.S > new file mode 100644 > index 000000000000..7c7fa45b5ab5 > --- /dev/null > +++ b/arch/riscv/lib/clear_page.S > @@ -0,0 +1,73 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > +/* > + * Copyright (c) 2023 Ventana Micro Systems Inc. > + */ > + > +#include <linux/linkage.h> > +#include <asm/asm.h> > +#include <asm/alternative-macros.h> > +#include <asm/hwcap.h> > +#include <asm/insn-def.h> > +#include <asm/page.h> > + > +#define CBOZ_ALT(order, old, new) \ > + ALTERNATIVE(old, new, 0, \ > + ((order) << 16) | RISCV_ISA_EXT_ZICBOZ, \ > + CONFIG_RISCV_ISA_ZICBOZ) > + > +/* void clear_page(void *page) */ > +ENTRY(__clear_page) > +WEAK(clear_page) out of interest, why the __clear_page() entry and the WEAK(clear_page)? Just followed up with a patch to fix the modpost. So far this seems to be working with qemu and a backport to 5.19.x
On Fri, Feb 24, 2023 at 02:00:44PM +0000, Ben Dooks wrote: > On 21/02/2023 19:09, Andrew Jones wrote: > > Using memset() to zero a 4K page takes 563 total instructions, where > > 20 are branches. clear_page(), with Zicboz and a 64 byte block size, > > takes 169 total instructions, where 4 are branches and 33 are nops. > > Even though the block size is a variable, thanks to alternatives, we > > can still implement a Duff device without having to do any preliminary > > calculations. This is achieved by using the alternatives' cpufeature > > value (the upper 16 bits of patch_id). The value used is the maximum > > zicboz block size order accepted at the patch site. This enables us > > to stop patching / unrolling when 4K bytes have been zeroed (we would > > loop and continue after 4K if the page size would be larger) > > > > For 4K pages, unrolling 16 times allows block sizes of 64 and 128 to > > only loop a few times and larger block sizes to not loop at all. Since > > cbo.zero doesn't take an offset, we also need an 'add' after each > > instruction, making the loop body 112 to 160 bytes. Hopefully this > > is small enough to not cause icache misses. > > > > Signed-off-by: Andrew Jones <ajones@ventanamicro.com> > > Acked-by: Conor Dooley <conor.dooley@microchip.com> > > --- > > arch/riscv/Kconfig | 13 ++++++ > > arch/riscv/include/asm/insn-def.h | 4 ++ > > arch/riscv/include/asm/page.h | 6 ++- > > arch/riscv/kernel/cpufeature.c | 11 +++++ > > arch/riscv/lib/Makefile | 1 + > > arch/riscv/lib/clear_page.S | 73 +++++++++++++++++++++++++++++++ > > 6 files changed, 107 insertions(+), 1 deletion(-) > > create mode 100644 arch/riscv/lib/clear_page.S > > [snip] > > > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c > > index 0594989ead63..4a496552b812 100644 > > --- a/arch/riscv/kernel/cpufeature.c > > +++ b/arch/riscv/kernel/cpufeature.c > > @@ -292,6 +292,17 @@ static bool riscv_cpufeature_patch_check(u16 id, u16 value) > > if (!value) > > return true; > > + switch (id) { > > + case RISCV_ISA_EXT_ZICBOZ: > > + /* > > + * Zicboz alternative applications provide the maximum > > + * supported block size order, or zero when it doesn't > > + * matter. If the current block size exceeds the maximum, > > + * then the alternative cannot be applied. > > + */ > > + return riscv_cboz_block_size <= (1U << value); > > + } > > + > > return false; > > } > > diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile > > index 6c74b0bedd60..26cb2502ecf8 100644 > > --- a/arch/riscv/lib/Makefile > > +++ b/arch/riscv/lib/Makefile > > @@ -8,5 +8,6 @@ lib-y += strlen.o > > lib-y += strncmp.o > > lib-$(CONFIG_MMU) += uaccess.o > > lib-$(CONFIG_64BIT) += tishift.o > > +lib-$(CONFIG_RISCV_ISA_ZICBOZ) += clear_page.o > > obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o > > diff --git a/arch/riscv/lib/clear_page.S b/arch/riscv/lib/clear_page.S > > new file mode 100644 > > index 000000000000..7c7fa45b5ab5 > > --- /dev/null > > +++ b/arch/riscv/lib/clear_page.S > > @@ -0,0 +1,73 @@ > > +/* SPDX-License-Identifier: GPL-2.0-only */ > > +/* > > + * Copyright (c) 2023 Ventana Micro Systems Inc. > > + */ > > + > > +#include <linux/linkage.h> > > +#include <asm/asm.h> > > +#include <asm/alternative-macros.h> > > +#include <asm/hwcap.h> > > +#include <asm/insn-def.h> > > +#include <asm/page.h> > > + > > +#define CBOZ_ALT(order, old, new) \ > > + ALTERNATIVE(old, new, 0, \ > > + ((order) << 16) | RISCV_ISA_EXT_ZICBOZ, \ > > + CONFIG_RISCV_ISA_ZICBOZ) > > + > > +/* void clear_page(void *page) */ > > +ENTRY(__clear_page) > > +WEAK(clear_page) > > out of interest, why the __clear_page() entry and the > WEAK(clear_page)? I was inspired by memset, but, in hindsight, it doesn't make sense for clear_page to be weak. > > Just followed up with a patch to fix the modpost. Thanks! > > So far this seems to be working with qemu and a backport to 5.19.x Great news! Thanks, drew
On Fri, Feb 24, 2023 at 03:25:30PM +0100, Andrew Jones wrote: > On Fri, Feb 24, 2023 at 02:00:44PM +0000, Ben Dooks wrote: > > On 21/02/2023 19:09, Andrew Jones wrote: ... > > > +/* void clear_page(void *page) */ > > > +ENTRY(__clear_page) > > > +WEAK(clear_page) > > > > out of interest, why the __clear_page() entry and the > > WEAK(clear_page)? > > I was inspired by memset, but, in hindsight, it doesn't make sense for > clear_page to be weak. Of course I failed to completely follow the memset pattern, which also has an export (in riscv_ksyms.c). I prefer the export in clear_page.S, though, as you've done. Thanks, drew
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 0c494c36e911..c9006bcf912d 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -456,6 +456,19 @@ config RISCV_ISA_ZICBOM If you don't know what to do here, say Y. +config RISCV_ISA_ZICBOZ + bool "Zicboz extension support for faster zeroing of memory" + depends on !XIP_KERNEL && MMU + select RISCV_ALTERNATIVE + default y + help + Enable the use of the ZICBOZ extension (cbo.zero instruction) + when available. + + The Zicboz extension is used for faster zeroing of memory. + + If you don't know what to do here, say Y. + config TOOLCHAIN_HAS_ZIHINTPAUSE bool default y diff --git a/arch/riscv/include/asm/insn-def.h b/arch/riscv/include/asm/insn-def.h index e01ab51f50d2..6960beb75f32 100644 --- a/arch/riscv/include/asm/insn-def.h +++ b/arch/riscv/include/asm/insn-def.h @@ -192,4 +192,8 @@ INSN_I(OPCODE_MISC_MEM, FUNC3(2), __RD(0), \ RS1(base), SIMM12(2)) +#define CBO_zero(base) \ + INSN_I(OPCODE_MISC_MEM, FUNC3(2), __RD(0), \ + RS1(base), SIMM12(4)) + #endif /* __ASM_INSN_DEF_H */ diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h index 9f432c1b5289..ccd168fe29d2 100644 --- a/arch/riscv/include/asm/page.h +++ b/arch/riscv/include/asm/page.h @@ -49,10 +49,14 @@ #ifndef __ASSEMBLY__ +#ifdef CONFIG_RISCV_ISA_ZICBOZ +void clear_page(void *page); +#else #define clear_page(pgaddr) memset((pgaddr), 0, PAGE_SIZE) +#endif #define copy_page(to, from) memcpy((to), (from), PAGE_SIZE) -#define clear_user_page(pgaddr, vaddr, page) memset((pgaddr), 0, PAGE_SIZE) +#define clear_user_page(pgaddr, vaddr, page) clear_page(pgaddr) #define copy_user_page(vto, vfrom, vaddr, topg) \ memcpy((vto), (vfrom), PAGE_SIZE) diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 0594989ead63..4a496552b812 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -292,6 +292,17 @@ static bool riscv_cpufeature_patch_check(u16 id, u16 value) if (!value) return true; + switch (id) { + case RISCV_ISA_EXT_ZICBOZ: + /* + * Zicboz alternative applications provide the maximum + * supported block size order, or zero when it doesn't + * matter. If the current block size exceeds the maximum, + * then the alternative cannot be applied. + */ + return riscv_cboz_block_size <= (1U << value); + } + return false; } diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile index 6c74b0bedd60..26cb2502ecf8 100644 --- a/arch/riscv/lib/Makefile +++ b/arch/riscv/lib/Makefile @@ -8,5 +8,6 @@ lib-y += strlen.o lib-y += strncmp.o lib-$(CONFIG_MMU) += uaccess.o lib-$(CONFIG_64BIT) += tishift.o +lib-$(CONFIG_RISCV_ISA_ZICBOZ) += clear_page.o obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o diff --git a/arch/riscv/lib/clear_page.S b/arch/riscv/lib/clear_page.S new file mode 100644 index 000000000000..7c7fa45b5ab5 --- /dev/null +++ b/arch/riscv/lib/clear_page.S @@ -0,0 +1,73 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (c) 2023 Ventana Micro Systems Inc. + */ + +#include <linux/linkage.h> +#include <asm/asm.h> +#include <asm/alternative-macros.h> +#include <asm/hwcap.h> +#include <asm/insn-def.h> +#include <asm/page.h> + +#define CBOZ_ALT(order, old, new) \ + ALTERNATIVE(old, new, 0, \ + ((order) << 16) | RISCV_ISA_EXT_ZICBOZ, \ + CONFIG_RISCV_ISA_ZICBOZ) + +/* void clear_page(void *page) */ +ENTRY(__clear_page) +WEAK(clear_page) + li a2, PAGE_SIZE + + /* + * If Zicboz isn't present, or somehow has a block + * size larger than 4K, then fallback to memset. + */ + CBOZ_ALT(12, "j .Lno_zicboz", "nop") + + lw a1, riscv_cboz_block_size + add a2, a0, a2 +.Lzero_loop: + CBO_zero(a0) + add a0, a0, a1 + CBOZ_ALT(11, "bltu a0, a2, .Lzero_loop; ret", "nop; nop") + CBO_zero(a0) + add a0, a0, a1 + CBOZ_ALT(10, "bltu a0, a2, .Lzero_loop; ret", "nop; nop") + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBOZ_ALT(9, "bltu a0, a2, .Lzero_loop; ret", "nop; nop") + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBOZ_ALT(8, "bltu a0, a2, .Lzero_loop; ret", "nop; nop") + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + CBO_zero(a0) + add a0, a0, a1 + bltu a0, a2, .Lzero_loop + ret +.Lno_zicboz: + li a1, 0 + tail __memset +END(__clear_page)