From: Jie Liu liujie375@h-partners.com

Add initial documentation for LSE support.

Signed-off-by: Jie Liu liujie375@h-partners.com Signed-off-by: Yicong Yang yangyicong@hisilicon.com --- .../WayCa-Kunpeng-LSE.md WayCa-Kunpeng-LSE.md | 282 ++++++++++++++++++ 1 file changed, 282 insertions(+) create mode 100644 WayCa-Kunpeng-底软/Wayca-Kunpeng-高性能调度/WayCa-Kunpeng-LSE.md WayCa-Kunpeng-LSE.md

diff --git a/WayCa-Kunpeng-底软/Wayca-Kunpeng-高性能调度/WayCa-Kunpeng-LSE.md WayCa-Kunpeng-LSE.md b/WayCa-Kunpeng-底软/Wayca-Kunpeng-高性能调度/WayCa-Kunpeng-LSE.md WayCa-Kunpeng-LSE.md new file mode 100644 index 0000000..35580da --- /dev/null +++ b/WayCa-Kunpeng-底软/Wayca-Kunpeng-高性能调度/WayCa-Kunpeng-LSE.md WayCa-Kunpeng-LSE.md @@ -0,0 +1,282 @@ +# WayCa-Kunpeng-LSE + +主线Linux及Openeuler均合入LSE的支持. + +目前Openeuler OLK-5.10已经合入了linux主线2021年前LSE相关patch。 + +## 1. LSE介绍 + +在编程时，如果多个处理器或线程访问共享数据，并且至少有一个正在写入时，操作必须是原 +子的。这意味着数据访问必须被视为相对于其他处理器的单独操作，以避免数据竞争。 + +微处理器的设计是将 read-modify-write和memory-register exchange等序列视为单独操作， +即使它们创建了对内存的多次访问，这种硬件使编程更容易。 + +在LSE之前的体系结构版本中，read-modify-write序列使用加载独占和存储独占指令。递增共 +享变量使用以下序列： +LDXR to read current count (load exclusive) +ADD to add one to the shared variable +STXR to attempt to store to memory (store exclusive) +CMP to check if the operation succeeded + +由于原子访问使用多个指令，每个处理器都需要实现独占监视器。独占监视器是一个硬件状态 +机，用于跟踪read-modify-write 序列并匹配加载和存储。如果处理器数量较少，则工作正 +常。增加处理器数量加上增加缓存，使得很难保持公平性，因为彼此更接近的处理器有更好的 +机会完成原子序列。 + +Armv8.1-A体系结构引入了新的原子指令，原子是加载的替代方案，存储以前体系结构版本中 +使用的独占序列。Arm体系结构参考手册将原子指令称为Large System Extensions (LSE)。 + +对于LSE，原子指令在单个指令中提供不可中断的read-modify-write序列。原子指令可以对 +指定的内存位置执行简单的算术或逻辑运算，并将更新后的值返回给处理器。程序员从原子指 +令中受益，因为与在序列失败时周围有循环的指令序列相比，指定单个指令更容易。LSE提高 +了具有许多处理器的系统中原子操作的性能。 + +LSE引入了一组原子指令： + +- 比较和交换指令, CAS and CASP. +- 原子内存操作指令, LD<OP> and ST<OP>, where <OP> is one of ADD, CLR, EOR, SET, + SMAX, SMIN, UMAX, and UMIN. +- 交换指令, SWP. + +LSE仅在A64中支持, 要求在Armv8.1及之后的版本必须实现. + +硬件通过ID_AA64ISAR0_EL1.Atomic (BITS[23:20])字段描述LSE的支持: + +- 0b0000: LSE原子指令不支持 +- 0b0010: 支持LDADD, LDCLR, LDEOR, LDSET, LDSMAX, LDSMIN, LDUMAX, LDUMIN, CAS, + CASP, and SWP 指令实施 + +0b0010表示硬件支持LSE, 从Armv8.1开始, 仅0b0010为合法值. + +## 2. 原子指令介绍 + +原子指令对一个内存位置执行原子读和写操作，使得体系结构保证在该指令定义的读和写之间， +另一个观察者不会对该内存位置进行修改。 + +### 2.1 原子内存操作 + +原子内存操作指令只支持一种寻址方式：base register only. 为了进行权限检查和观察点， +所有原子内存操作指令都被视为执行加载和存储。如果未实现LSE2，则LD<OP>和ST<OP>指令需 +要自然对齐，而未对齐的地址会生成对齐错误。 + +这些指令提供了排序选项，这些选项映射到体系结构中使用的acquire和release定义。具有 +release语义的原子指令与Store-Release指令在多副本原子性方面具有相同的规则。这些操 +作映射到acquire和release定义，并分别计算为Load-Acquire和tore-Release操作。 + +对于LD<OP>指令，当源寄存器和目标寄存器相同时，如果指令生成同步数据中止，则源寄存器 +将恢复到指令执行前保持的值。 + +ST<OP>指令和目标寄存器为WZR或XZR的LD<OP>指令不被视为在做用于DMB LD barrier的读取。 + +| Mnemonic | Instruction | See | +| ------ | ---------- | :----- | +| LDADD | Atomic add | LDADD, LDADDA, LDADDAL, LDADDL | +| LDADDB | Atomic add on byte | LDADDB, LDADDAB, LDADDALB, LDADDLB | +| LDADDH | Atomic add on halfword | LDADDH, LDADDAH, LDADDALH, LDADDLH | +| LDCLR | Atomic bit clear | LDCLR, LDCLRA, LDCLRAL, LDCLRL | +| LDCLRB | Atomic bit clear on byte | LDCLRB, LDCLRAB, LDCLRALB, LDCLRLB | +| LDCLRH | Atomic bit clear on halfword | LDCLRH, LDCLRAH, LDCLRALH, LDCLRLH | +| LDEOR | Atomic exclusive OR | LDEOR, LDEORA, LDEORAL, LDEORL | +| LDEORB | Atomic exclusive OR on byte | LDEORB, LDEORAB, LDEORALB, LDEORLB | +| LDEORH | Atomic exclusive OR on halfword | LDEORH, LDEORAH, LDEORALH, LDEORLH | +| LDSET | Atomic bit set | LDSET, LDSETA, LDSETAL, LDSETL | +| LDSETB | Atomic bit set on byte | LDSETB, LDSETAB, LDSETALB, LDSETLB | +| LDSETH | Atomic bit set on halfword | LDSETH, LDSETAH, LDSETALH, LDSETLH | +| LDMAX | Atomic signed maximum | LDSMAX, LDSMAXA, LDSMAXAL, LDSMAXL | +| LDMAXB | Atomic signed maximum on byte | LDSMAXB, LDSMAXAB, LDSMAXALB, LDSMAXLB | +| LDMAXH | Atomic signed maximum on halfword | LDSMAXH, LDSMAXAH, LDSMAXALH, LDSMAXLH | +| LDMIN | Atomic signed minimum | LDSMIN, LDSMINA, LDSMINAL, LDSMINL | +| LDMINB | Atomic signed minimum on byte | LDSMINB, LDSMINAB, LDSMINALB, LDSMINLB | +| LDMINH | Atomic signed minimum on halfword | LDSMINH, LDSMINAH, LDSMINALH, LDSMINLH | +| LDUMAX | Atomic unsigned maximum | LDUMAX, LDUMAXA, LDUMAXAL, LDUMAXL | +| LDUMAXB | Atomic unsigned maximum on byte | LDUMAXB, LDUMAXAB, LDUMAXALB, LDUMAXLB | +| LDUMAXH | Atomic unsigned maximum on halfword | LDUMAXH, LDUMAXAH, LDUMAXALH, LDUMAXLH | +| LDUMIN | Atomic unsigned minimum | LDUMIN, LDUMINA, LDUMINAL, LDUMINL | +| LDUMINB | Atomic unsigned minimum on byte | LDUMINB, LDUMINAB, LDUMINALB, LDUMINLB | +| LDUMINH | Atomic unsigned minimum on halfword | LDUMINH, LDUMINAH, LDUMINALH, LDUMINLH | +| STADD | Atomic add, without return | STADD, STADDL | +| STADDB | Atomic add on byte, without return | STADDB, STADDLB | +| STADDH | Atomic add on halfword, without return | STADDH, STADDLH | +| STCLR | Atomic bit clear, without return | STCLR, STCLRL | +| STCLRB | Atomic bit clear on byte, without return | STCLRB, STCLRLB | +| STCLRH | Atomic bit clear on halfword, without return | STCLRH, STCLRLH | +| STEOR | Atomic exclusive OR, without return | STEOR, STEORL | +| STEORB | Atomic exclusive OR on byte, without return | STEORB, STEORLB | +| STEORH | Atomic exclusive OR on halfword, without return | STEORH, STEORLH | +| STSET | Atomic bit set, without return | STSET, STSETL | +| STSETB | Atomic bit set on byte, without return | STSETB, STSETLB | +| STSETH | Atomic bit set on halfword, without return | STSETH, STSETLH | +| STMAX | Atomic signed maximum, without return | STSMAX, STSMAXL | +| STMAXB | Atomic signed maximum on byte, without return | STSMAXB, STSMAXLB | +| STMAXH | Atomic signed maximum on halfword, without return | STSMAXH, STSMAXLH | +| STMIN | Atomic signed minimum, without return | STSMIN, STSMINL | +| STMINB | Atomic signed minimum on byte, without return | STSMINB, STSMINLB | +| STMINH | Atomic signed minimum on halfword, without return | STSMINH, STSMINLH | +| STUMAX | Atomic unsigned maximum, without return | STUMAX, STUMAXL | +| STUMAXB | Atomic unsigned maximum on byte, without return | STUMAXB, STUMAXLB | +| STUMAXH | Atomic unsigned maximum on halfword,without return | STUMAXH, STUMAXLH | +| STUMIN | Atomic unsigned minimum, without return | STUMIN, STUMINL | +| STUMINB | Atomic unsigned minimum on byte, without return | STUMINB, STUMINLB | +| STUMINH | Atomic unsigned minimum on halfword,without return | STUMINH, STUMINLH | + +### 2.2 Swap + +交换指令仅支持一种寻址模式：Base register only。为了进行权限检查和观察点，所有交换 +指令都被视为执行加载和存储。如果未实现FEAT_LSE2，则SWP指令需要自然对齐，而未对齐的 +地址会生成对齐错误。 + +这些指令提供了排序选项，这些选项映射到体系结构中使用的acquire和release定义。具有 +release语义的原子指令与Store-Release指令在多副本原子性方面具有相同的规则。 + +对于SWP指令，源寄存器和目标寄存器相同，如果指令生成同步数据中止，则源寄存器将恢复 +到指令执行前保持的值。 + +| Mnemonic | Instruction | See | +| -------- | ------------- | -------------------------- | +| SWP | Swap | SWP, SWPA, SWPAL, SWPL | +| SWPB | Swap byte | SWPB, SWPAB, SWPALB, SWPLB | +| SWPH | Swap halfword | SWPB, SWPAB, SWPALB, SWPLB | + +### 2.3 Compare and Swap + +比较与交换指令仅支持一种寻址模式：Base register only。为了进行权限检查和观察点， +所有比较与交换指令都被视为执行加载和存储。如果未实现FEAT_LSE2，则CAS指令要求自然 +对齐，CASP指令要求与所访问的内存的总大小对齐。 + +这些指令提供了排序选项，这些选项映射到体系结构中使用的acquire和release定义。如果 +比较和交换指令不执行存储，则无论指令排序选项如何，该指令都没有release语义。具有 +release语义的原子指令与Store-Release指令在多副本原子性方面具有相同的规则。 + +对于CAS和CASP指令，体系结构允许数据读取清除与该位置有关联的任何独占监视器，即使 +比较随后失败。如果这些指令生成同步数据中止，被比较和加载的寄存器恢复到指令执行之 +前保存的值。 + +| Mnemonic | Instruction | See | +| -------- | ------------------------- | -------------------------- | +| CAS | Compare and swap | CAS, CASA, CASAL, CASL | +| CASB | Compare and swap byte | CASB, CASAB, CASALB, CASLB | +| CASH | Compare and swap halfword | CASH, CASAH, CASALH, CASLH | +| CASP | Compare and swap pair | CASP, CASPA, CASPAL, CASPL | + +## 3. 内核配置支持 + +### 3.1 内核配置 + +使能LSE需要开启以下内核配置: + +- CONFIG_ARM64_LSE_ATOMICS +- CONFIG_ARM64_USE_LSE_ATOMICS (depends on CONFIG_JUMP_LABEL) + +目前在openeuler_defconfig中，配置均默认打开: + +``` +CONFIG_ARM64_LSE_ATOMICS=y +CONFIG_ARM64_USE_LSE_ATOMICS=y +``` + +### 3.2 编译器支持 + +LSE使能需要编译器支持. + +- GCC + +当使用GCC编译器时, 需要支持以下选项: + +``` +-moutline-atomics +-mno-outline-atomics +``` + +以上配置帮助程序将在运行时确定是否可以使用ARMv8.1-A中的LSE指令；如果不能，他们将 +使用基本ARMv8.0 ISA中存在的load/store-exclusive指令。 + +此选项仅适用于为基本ARMv8.0指令集编译时。如果使用较高的版本，例如-march=armv8.1-a +或-march=Armv8-a+lse，则将直接使用ARMv8.1-原子指令。当所选CPU支持“lse”功能时，使用-mcpu=lse也可以。默认情况下，此选项处于打开状态。 + +- Clang + +当使用Clang编译器是, 需要支持-march=lse选项. + +> [NOTE] +> commit e0d5896bd356 和 commit dd1f6308b28e修复了clang编译时使用lse的错误。 + +## 4. 软件接口 + +- 用户可以通过/proc/cpuinfo或HWCAP查询硬件对于LSE的支持情况. + +## 5. 涉及代码和使能 + +| Commit id | Subject | openeuler OLK5.10 enabled（Y/N） | +| ------------ | ------------------------------------------------------------ | -------------------------------- | +| 9511ca19dafb | arm64: rwlocks: don't fail trylock purely due to contention | Y | +| 144e9697a9e7 | arm64: cpufeature.h: add missing #include of kernel.h | Y | +| c275f76bb4ce | arm64: atomics: move ll/sc atomics into separate header file | Y | +| 40a1db2434a1 | arm64: elf: advertise 8.1 atomic instructions as new hwcap | Y | +| d964b7229e7f | arm64: alternatives: add cpu feature for lse atomics | Y | +| c0385b24af15 | arm64: introduce CONFIG_ARM64_LSE_ATOMICS as fallback to ll/sc atomics | Y | +| c09d6a04d17d | arm64: atomics: patch in lse instructions when supported by the CPU | Y | +| 81bb5c642063 | arm64: locks: patch in lse instructions when supported by the CPU | Y | +| 084f903727e1 | arm64: bitops: patch in lse instructions when supported by the CPU | Y | +| c8366ba0fb65 | arm64: xchg: patch in lse instructions when supported by the CPU | Y | +| c342f78217e8 | arm64: cmpxchg: patch in lse instructions when supported by the CPU | Y | +| e9a4b795652f | arm64: cmpxchg_dbl: patch in lse instructions when supported by the CPU | Y | +| 0bc671d3f4be | arm64: cmpxchg: avoid "cc" clobber in ll/sc routines | Y | +| 4e39715f4b5c | arm64: cmpxchg: avoid memory barrier on comparison failure | Y | +| a82e62382fcb | arm64: atomics: tidy up common atomic{,64}_* macros | Y | +| 0ea366f5e1b6 | arm64: atomics: prefetch the destination word for write prior to stxr | Y | +| 6059a7b6e818 | arm64: atomics: implement atomic{,64}_cmpxchg using cmpxchg | Y | +| db26217e6f54 | arm64: atomic64_dec_if_positive: fix incorrect branch condition | Y | +| 95eff6b27c40 | arm64: kconfig: select HAVE_CMPXCHG_LOCAL | Y | +| c739dc83a0b6 | arm64: lse: rename ARM64_CPU_FEAT_LSE_ATOMICS for consistency | Y | +| 0e4a07092fc8 | arm64: kconfig: group the v8.1 features together | Y | +| 2e94da137903 | arm64: lse: use generic cpufeature detection for LSE atomics | Y | +| c1d7cd228b4b | arm64: spinlock: fix ll/sc unlock on big-endian systems | Y | +| 484c96dbb269 | arm64: lse: fix lse cmpxchg code indentation | Y | +| 7f08a414f29e | arm64: make ll/sc __cmpxchg_case_##name asm consistent | Y | +| 305d454aaa29 | arm64: atomics: implement native {relaxed, acquire, release} atomics | Y | +| da8d02d19ffd | arm64/capabilities: Make use of system wide safe value | Y | +| 57a65667991a | arm64: cmpxchg_dbl: fix return value type | Y | +| d86b8da04dfa | arm64: spinlock: serialise spin_unlock_wait against concurrent lockers | Y | +| cd5e10bdf379 | arm64: prefetch: don't provide spin_lock_prefetch with LSE | Y | +| ff96f7bc7bf6 | arm64: capabilities: Handle sign of the feature bit | Y | +| 5be8b70af1ca | arm64: lse: deal with clobbered IP registers after branch via PLT | Y | +| 3a5facd09da8 | arm64: spinlock: fix spin_unlock_wait for LSE atomics | Y | +| e490f9b1d3b4 | locking/atomic, arch/arm64: Implement atomic{,64}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}() | Y | +| 6822a84dd4e3 | locking/atomic, arch/arm64: Generate LSE non-return cases using common macros | Y | +| 2efe95fe6952 | locking/atomic, arch/arm64: Implement atomic{,64}_fetch_add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}() for LSE instructions | Y | +| efd9e03facd0 | arm64: Use static keys for CPU features | Y | +| 05492f2fd87d | arm64: lse: convert lse alternatives NOP padding to use __nops | Y | +| 272d01bd790f | arm64: Fix circular include of asm/lse.h through linux/jump_label.h | Y | +| b7eed6ddaa71 | arm64: do not trace atomic operations | Y | +| 8997c93452d1 | arm64: atomic_lse: match asm register sizes | Y | +| 8df728e1ae61 | arm64: Remove redundant mov from LL/SC cmpxchg | Y | +| 32fb5d73c98b | arm64: atomics: Remove '&' from '+&' asm constraint in lse atomics | Y | +| 6b24442d68e7 | arm64: lse: Pass -fomit-frame-pointer to out-of-line ll/sc atomics | Y | +| 5b4747c5dce7 | arm64: capabilities: Add flags to handle the conflicts on late CPU | Y | +| 8a624f145c0d | arm64: lse: Include compiler_types.h and export.h for out-of-line LL/SC | Y | +| 32c3fa7cdf0c | arm64: lse: Add early clobbers to some input/output asm operands | Y | +| 7bd99b403405 | arm64: Kconfig: Enable LSE atomics by default | Y | +| 7c8fc35dfc32 | locking/atomics/arm64: Replace our atomic/lock bitop implementations with asm-generic | Y | +| 356c6fe7d80c | locking/atomics/arm64, arm64/bitops: Include <asm-generic/bitops/ext2-atomic-setbit.h | Y | +| 2a6c7c367de8 | arm64: lse: remove -fcall-used-x0 flag | Y | +| c0df10812835 | arm64, locking/atomics: Use instrumented atomics | Y | +| 5ef3fe4cecdf | arm64: Avoid redundant type conversions in xchg() and cmpxchg() | Y | +| b4f9209bfcd5 | arm64: Avoid masking "old" for LSE cmpxchg() implementation | Y | +| 959bf2fd03b5 | arm64: percpu: Rewrite per-cpu ops to allow use of LSE atomics | Y | +| 4230509978f2 | arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint | Y | +| 6e4ede698d1c | arm64: percpu: Fix LSE implementation of value-returning pcpu atomics | Y | +| 34b8ab091f9e | bpf, arm64: use more scalable stadd over ldxr / stxr loop in xadd | Y | +| 16f18688af7e | locking/atomic, arm64: Use s64 for atomic64 | Y | +| 580fa1b87471 | arm64: Use correct ll/sc atomic constraints | Y | +| addfc38672c7 | arm64: atomics: avoid out-of-line ll/sc atomics | Y | +| 3337cb5aea59 | arm64: avoid using hard-coded registers for LSE atomics | Y | +| eb3aabbfbfc2 | arm64: atomics: Remove atomic_ll_sc compilation unit | Y | +| 0ca98b2456fb | arm64: lse: Remove unused 'alt_lse' assembly macro | Y | +| 0533f97b4356 | arm64: asm: Kill 'asm/atomic_arch.h' | Y | +| b32baf91f60f | arm64: lse: Make ARM64_LSE_ATOMICS depend on JUMP_LABEL | Y | +| 03adcbd996be | arm64: atomics: Use K constraint when toolchain appears to support it | Y | +| a48e61de758c | arm64: Mark functions using explicit register variables as '__always_inline' | Y | +| 395af861377d | arm64: Move the LSE gas support detection to Kconfig | Y | +| e0d5896bd356 | arm64: lse: fix LSE atomics with LLVM's integrated assembler | Y | +| dd1f6308b28e | arm64: lse: Fix LSE atomics with LLVM | Y |