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[62.178.148.172]) by smtp.gmail.com with ESMTPSA id f1-20020a1cc901000000b003df14531724sm16862050wmb.21.2023.02.06.16.16.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Feb 2023 16:16:57 -0800 (PST) From: Christoph Muellner To: libc-alpha@sourceware.org, Palmer Dabbelt , Darius Rad , Andrew Waterman , DJ Delorie , Vineet Gupta , Kito Cheng , Jeff Law , Philipp Tomsich , Heiko Stuebner Cc: =?UTF-8?q?Christoph=20M=C3=BCllner?= Subject: [RFC PATCH 19/19] riscv: Add __riscv_cpu_relax() to allow yielding in busy loops Date: Tue, 7 Feb 2023 01:16:18 +0100 Message-Id: <20230207001618.458947-20-christoph.muellner@vrull.eu> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230207001618.458947-1-christoph.muellner@vrull.eu> References: <20230207001618.458947-1-christoph.muellner@vrull.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,JMQ_SPF_NEUTRAL,KAM_MANYTO,KAM_SHORT,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: From: Christoph Müllner The spinning loop of PTHREAD_MUTEX_ADAPTIVE_NP provides the hook atomic_spin_nop() that can be used by architectures. On RISC-V we have two instructions that can be used here: * WRS.STO from the Zawrs extension * PAUSE from the Zihintpause extension Let's use these instructions and prefer WRS.STO over PAUSE (based on availability of the corresponding ISA extension at runtime). Signed-off-by: Christoph Müllner --- sysdeps/riscv/multiarch/Makefile | 5 +++ sysdeps/riscv/multiarch/cpu_relax.c | 36 +++++++++++++++++ sysdeps/riscv/multiarch/cpu_relax_impl.S | 40 +++++++++++++++++++ .../unix/sysv/linux/riscv/atomic-machine.h | 3 ++ 4 files changed, 84 insertions(+) create mode 100644 sysdeps/riscv/multiarch/cpu_relax.c create mode 100644 sysdeps/riscv/multiarch/cpu_relax_impl.S diff --git a/sysdeps/riscv/multiarch/Makefile b/sysdeps/riscv/multiarch/Makefile index 9f22e31b99..b5b9fcf986 100644 --- a/sysdeps/riscv/multiarch/Makefile +++ b/sysdeps/riscv/multiarch/Makefile @@ -17,3 +17,8 @@ sysdep_routines += \ strncmp_generic \ strncmp_zbb endif + +# nscd uses atomic_spin_nop which in turn requires cpu_relax +ifeq ($(subdir),nscd) +routines += cpu_relax cpu_relax_impl +endif diff --git a/sysdeps/riscv/multiarch/cpu_relax.c b/sysdeps/riscv/multiarch/cpu_relax.c new file mode 100644 index 0000000000..4e6825ca50 --- /dev/null +++ b/sysdeps/riscv/multiarch/cpu_relax.c @@ -0,0 +1,36 @@ +/* CPU strand yielding for busy loops. RISC-V version. + Copyright (C) 2022 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include + +void __cpu_relax (void); +extern void __cpu_relax_zawrs (void); +extern void __cpu_relax_zihintpause (void); + +static void +__cpu_relax_generic (void) +{ +} + +libc_ifunc (__cpu_relax, + HAVE_RV(zawrs) + ? __cpu_relax_zawrs + : HAVE_RV(zihintpause) + ? __cpu_relax_zihintpause + : __cpu_relax_generic); diff --git a/sysdeps/riscv/multiarch/cpu_relax_impl.S b/sysdeps/riscv/multiarch/cpu_relax_impl.S new file mode 100644 index 0000000000..5d349c351f --- /dev/null +++ b/sysdeps/riscv/multiarch/cpu_relax_impl.S @@ -0,0 +1,40 @@ +/* Copyright (C) 2022 Free Software Foundation, Inc. + + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library. If not, see + . */ + +#include +#include + +.option push +.option arch,+zawrs + +ENTRY_ALIGN (__cpu_relax_zawrs, 4) + wrs.sto + ret +END (__cpu_relax_zawrs) + +.option pop + +.option push +.option arch,+zihintpause + +ENTRY_ALIGN (__cpu_relax_zihintpause, 4) + pause + ret +END (__cpu_relax_zihintpause) + +.option pop diff --git a/sysdeps/unix/sysv/linux/riscv/atomic-machine.h b/sysdeps/unix/sysv/linux/riscv/atomic-machine.h index dbf70d8d57..88aa58ef95 100644 --- a/sysdeps/unix/sysv/linux/riscv/atomic-machine.h +++ b/sysdeps/unix/sysv/linux/riscv/atomic-machine.h @@ -178,4 +178,7 @@ # error "ISAs that do not subsume the A extension are not supported" #endif /* !__riscv_atomic */ +extern void __cpu_relax (void); +#define atomic_spin_nop() __cpu_relax() + #endif /* bits/atomic.h */ -- 2.39.1