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Date: Fri, 12 Aug 2022 06:57:47 +0000
From: <Conor.Dooley@...rochip.com>
To: <palmer@...belt.com>, <daolu@...osinc.com>
CC: <linux-kernel@...r.kernel.org>, <heiko@...ech.de>,
<paul.walmsley@...ive.com>, <aou@...s.berkeley.edu>,
<atishp@...shpatra.org>, <anup@...infault.org>,
<guoren@...nel.org>, <jszhang@...nel.org>, <rdunlap@...radead.org>,
<niklas.cassel@....com>, <panqinglin2020@...as.ac.cn>,
<alexandre.ghiti@...onical.com>, <robh@...nel.org>,
<research_trasio@....a4lg.com>, <yury.norov@...il.com>,
<linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v4] arch/riscv: add Zihintpause support
On 11/08/2022 16:17, Palmer Dabbelt wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>
> On Mon, 20 Jun 2022 13:15:25 PDT (-0700), daolu@...osinc.com wrote:
>> Implement support for the ZiHintPause extension.
>>
>> The PAUSE instruction is a HINT that indicates the current hart’s rate
>> of instruction retirement should be temporarily reduced or paused.
>>
>> Reviewed-by: Heiko Stuebner <heiko@...ech.de>
>> Tested-by: Heiko Stuebner <heiko@...ech.de>
>> Signed-off-by: Dao Lu <daolu@...osinc.com>
>> ---
>>
>> v1 -> v2:
>> Remove the usage of static branch, use PAUSE if toolchain supports it
>> v2 -> v3:
>> Added the static branch back, cpu_relax() behavior is kept the same for
>> systems that do not support ZiHintPause
>> v3 -> v4:
>> Adopted the newly added unified static keys for extensions
>> ---
>> arch/riscv/Makefile | 4 ++++
>> arch/riscv/include/asm/hwcap.h | 5 +++++
>> arch/riscv/include/asm/vdso/processor.h | 21 ++++++++++++++++++---
>> arch/riscv/kernel/cpu.c | 1 +
>> arch/riscv/kernel/cpufeature.c | 1 +
>> 5 files changed, 29 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>> index 34cf8a598617..6ddacc6f44b9 100644
>> --- a/arch/riscv/Makefile
>> +++ b/arch/riscv/Makefile
>> @@ -56,6 +56,10 @@ riscv-march-$(CONFIG_RISCV_ISA_C) := $(riscv-march-y)c
>> toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
>> riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
>>
>> +# Check if the toolchain supports Zihintpause extension
>> +toolchain-supports-zihintpause := $(call cc-option-yn, -march=$(riscv-march-y)_zihintpause)
>> +riscv-march-$(toolchain-supports-zihintpause) := $(riscv-march-y)_zihintpause
>> +
>> KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
>> KBUILD_AFLAGS += -march=$(riscv-march-y)
>>
>> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
>> index e48eebdd2631..dc47019a0b38 100644
>> --- a/arch/riscv/include/asm/hwcap.h
>> +++ b/arch/riscv/include/asm/hwcap.h
>> @@ -8,6 +8,7 @@
>> #ifndef _ASM_RISCV_HWCAP_H
>> #define _ASM_RISCV_HWCAP_H
>>
>> +#include <asm/errno.h>
>> #include <linux/bits.h>
>> #include <uapi/asm/hwcap.h>
>>
>> @@ -54,6 +55,7 @@ extern unsigned long elf_hwcap;
>> enum riscv_isa_ext_id {
>> RISCV_ISA_EXT_SSCOFPMF = RISCV_ISA_EXT_BASE,
>> RISCV_ISA_EXT_SVPBMT,
>> + RISCV_ISA_EXT_ZIHINTPAUSE,
>> RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
>> };
>>
>> @@ -64,6 +66,7 @@ enum riscv_isa_ext_id {
>> */
>> enum riscv_isa_ext_key {
>> RISCV_ISA_EXT_KEY_FPU, /* For 'F' and 'D' */
>> + RISCV_ISA_EXT_KEY_ZIHINTPAUSE,
>> RISCV_ISA_EXT_KEY_MAX,
>> };
>>
>> @@ -83,6 +86,8 @@ static __always_inline int riscv_isa_ext2key(int num)
>> return RISCV_ISA_EXT_KEY_FPU;
>> case RISCV_ISA_EXT_d:
>> return RISCV_ISA_EXT_KEY_FPU;
>> + case RISCV_ISA_EXT_ZIHINTPAUSE:
>> + return RISCV_ISA_EXT_KEY_ZIHINTPAUSE;
>> default:
>> return -EINVAL;
>> }
>> diff --git a/arch/riscv/include/asm/vdso/processor.h b/arch/riscv/include/asm/vdso/processor.h
>> index 134388cbaaa1..1e4f8b4aef79 100644
>> --- a/arch/riscv/include/asm/vdso/processor.h
>> +++ b/arch/riscv/include/asm/vdso/processor.h
>> @@ -4,15 +4,30 @@
>>
>> #ifndef __ASSEMBLY__
>>
>> +#include <linux/jump_label.h>
>> #include <asm/barrier.h>
>> +#include <asm/hwcap.h>
>>
>> static inline void cpu_relax(void)
>> {
>> + if (!static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_ZIHINTPAUSE])) {
>> #ifdef __riscv_muldiv
>> - int dummy;
>> - /* In lieu of a halt instruction, induce a long-latency stall. */
>> - __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
>> + int dummy;
>> + /* In lieu of a halt instruction, induce a long-latency stall. */
>> + __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
>> #endif
>> + } else {
>> + /*
>> + * Reduce instruction retirement.
>> + * This assumes the PC changes.
>> + */
>> +#ifdef __riscv_zihintpause
>> + __asm__ __volatile__ ("pause");
>> +#else
>> + /* Encoding of the pause instruction */
>> + __asm__ __volatile__ (".4byte 0x100000F");
>> +#endif
>> + }
>> barrier();
>> }
>>
>> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
>> index fba9e9f46a8c..a123e92b14dd 100644
>> --- a/arch/riscv/kernel/cpu.c
>> +++ b/arch/riscv/kernel/cpu.c
>> @@ -89,6 +89,7 @@ int riscv_of_parent_hartid(struct device_node *node)
>> static struct riscv_isa_ext_data isa_ext_arr[] = {
>> __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
>> __RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
>> + __RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
>> __RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
>> };
>>
>> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
>> index 1b3ec44e25f5..708df2c0bc34 100644
>> --- a/arch/riscv/kernel/cpufeature.c
>> +++ b/arch/riscv/kernel/cpufeature.c
>> @@ -198,6 +198,7 @@ void __init riscv_fill_hwcap(void)
>> } else {
>> SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
>> SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
>> + SET_ISA_EXT_MAP("zihintpause", RISCV_ISA_EXT_ZIHINTPAUSE);
>> }
>> #undef SET_ISA_EXT_MAP
>> }
>
> Thanks, this is on for-next. It needs a sparse patch, which I put in as a link.
This breaks the C=1 build for all toolchains, not just new ones as your sparse
patch suggests. I amn't 100% what my CI is running, but I replicated this on
my own machine with:
sparse --version
0.6.4 (Ubuntu: 0.6.4-2)
---8<---
YACC scripts/dtc/dtc-parser.tab.[ch]
HOSTCC scripts/dtc/libfdt/fdt.o
HOSTCC scripts/dtc/libfdt/fdt_ro.o
HOSTCC scripts/dtc/libfdt/fdt_wip.o
UPD include/generated/uapi/linux/version.h
HOSTCC scripts/dtc/libfdt/fdt_sw.o
UPD include/config/kernel.release
HOSTCC scripts/dtc/libfdt/fdt_rw.o
HOSTCC scripts/dtc/libfdt/fdt_strerror.o
HOSTCC scripts/dtc/libfdt/fdt_empty_tree.o
HOSTCC scripts/dtc/libfdt/fdt_addresses.o
HOSTCC scripts/dtc/libfdt/fdt_overlay.o
HOSTCC scripts/dtc/fdtoverlay.o
HOSTCC scripts/dtc/dtc-lexer.lex.o
HOSTCC scripts/dtc/dtc-parser.tab.o
UPD include/generated/utsrelease.h
HOSTLD scripts/dtc/fdtoverlay
HOSTLD scripts/dtc/dtc
HOSTCC scripts/kallsyms
HOSTCC scripts/sorttable
HOSTCC scripts/asn1_compiler
HOSTCC scripts/selinux/genheaders/genheaders
HOSTCC scripts/selinux/mdp/mdp
CC scripts/mod/empty.o
HOSTCC scripts/mod/mk_elfconfig
CC scripts/mod/devicetable-offsets.s
CHECK ../scripts/mod/empty.c
invalid argument to '-march': '_zihintpause'
make[2]: *** [../scripts/Makefile.build:250: scripts/mod/empty.o] Error 1
make[2]: *** Deleting file 'scripts/mod/empty.o'
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/mnt/automation/corp/workspace/ux-test_upstream-next-develop-cd@...inux/Makefile:1287: prepare0] Error 2
make[1]: Leaving directory '/mnt/automation/corp/workspace/ux-test_upstream-next-develop-cd@...inux/builddir'
make: *** [Makefile:231: __sub-make] Error 2
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