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Wed, 13 Mar 2024 14:31:25 +0000 From: Wilco Dijkstra To: 'GNU C Library' Subject: [PATCH] AArch64: Check kernel version for SVE ifuncs Thread-Topic: [PATCH] AArch64: Check kernel version for SVE ifuncs Thread-Index: AQHadVLx33HAZ4D2skuZZ4SgsA+U6w== Date: Wed, 13 Mar 2024 14:31:25 +0000 Message-ID: Accept-Language: en-GB, en-US Content-Language: en-GB X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; x-ms-traffictypediagnostic: PAWPR08MB8982:EE_|PA4PR08MB7595:EE_|DB5PEPF00014B98:EE_|DU2PR08MB10085:EE_ X-MS-Office365-Filtering-Correlation-Id: 9cf54599-ca7b-449c-4ec3-08dc436a4818 x-checkrecipientrouted: true nodisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: 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 X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255; 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Calling the SVE-optimized memcpy afterwards will then cause a trap to reenable SVE. As a result, applications with a high use of syscalls may run slower with the SVE memcpy. Avoid this by checking the kernel version and enable the SVE-optimized memcpy/memmove ifuncs only on Linux kernel 6.2 or newer. Passes regress, OK for commit? diff --git a/sysdeps/aarch64/cpu-features.h b/sysdeps/aarch64/cpu-features.h index 77a782422af1b6e4b2af32bfebfda37874111510..5f2da91ebbd0adafb0d84ec503b0f902f566da5a 100644 --- a/sysdeps/aarch64/cpu-features.h +++ b/sysdeps/aarch64/cpu-features.h @@ -71,6 +71,7 @@ struct cpu_features /* Currently, the GLIBC memory tagging tunable only defines 8 bits. */ uint8_t mte_state; bool sve; + bool prefer_sve_ifuncs; bool mops; }; diff --git a/sysdeps/aarch64/multiarch/init-arch.h b/sysdeps/aarch64/multiarch/init-arch.h index c52860efb22d70eb4bdf356781f51c7de8ec67dc..61dc40088f4d9e5e06b57bdc7d54bde1e2a686a4 100644 --- a/sysdeps/aarch64/multiarch/init-arch.h +++ b/sysdeps/aarch64/multiarch/init-arch.h @@ -36,5 +36,7 @@ MTE_ENABLED (); \ bool __attribute__((unused)) sve = \ GLRO(dl_aarch64_cpu_features).sve; \ + bool __attribute__((unused)) prefer_sve_ifuncs = \ + GLRO(dl_aarch64_cpu_features).prefer_sve_ifuncs; \ bool __attribute__((unused)) mops = \ GLRO(dl_aarch64_cpu_features).mops; diff --git a/sysdeps/aarch64/multiarch/memcpy.c b/sysdeps/aarch64/multiarch/memcpy.c index d12eccfca51f4bcfef6ccf5aa286edb301e361ac..ce53567dab33c2f00b89b4069235abd4651811a6 100644 --- a/sysdeps/aarch64/multiarch/memcpy.c +++ b/sysdeps/aarch64/multiarch/memcpy.c @@ -47,7 +47,7 @@ select_memcpy_ifunc (void) { if (IS_A64FX (midr)) return __memcpy_a64fx; - return __memcpy_sve; + return prefer_sve_ifuncs ? __memcpy_sve : __memcpy_generic; } if (IS_THUNDERX (midr)) diff --git a/sysdeps/aarch64/multiarch/memmove.c b/sysdeps/aarch64/multiarch/memmove.c index 2081eeb4d40e0240e67a7b26b64576f44eaf18e3..fe95037be391896c7670ef606bf4d3ba7dfb6a00 100644 --- a/sysdeps/aarch64/multiarch/memmove.c +++ b/sysdeps/aarch64/multiarch/memmove.c @@ -47,7 +47,7 @@ select_memmove_ifunc (void) { if (IS_A64FX (midr)) return __memmove_a64fx; - return __memmove_sve; + return prefer_sve_ifuncs ? __memmove_sve : __memmove_generic; } if (IS_THUNDERX (midr)) diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c index b1a3f673f067280bdacfddd92723a81e418023e5..13b02c45df80b493516b3c9d4acbbbffaa47af92 100644 --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c @@ -21,6 +21,7 @@ #include #include #include +#include #include #define DCZID_DZP_MASK (1 << 4) @@ -62,6 +63,41 @@ get_midr_from_mcpu (const struct tunable_str_t *mcpu) return UINT64_MAX; } +/* Parse kernel version without calling any library functions. + Allow 2 digits for kernel version and 3 digits for major version, + separated by '.': "kk.mmm.". + Return kernel version * 1000 + major version, or -1 on failure. */ + +static inline int +kernel_version (void) +{ + struct utsname buf; + const char *p = &buf.release[0]; + int kernel = 0; + int major = 0; + + if (__uname (&buf) < 0) + return -1; + + if (*p >= '0' && *p <= '9') + kernel = (kernel * 10) + *p++ - '0'; + if (*p >= '0' && *p <= '9') + kernel = (kernel * 10) + *p++ - '0'; + if (*p != '.') + return -1; + p++; + if (*p >= '0' && *p <= '9') + major = (major * 10) + *p++ - '0'; + if (*p >= '0' && *p <= '9') + major = (major * 10) + *p++ - '0'; + if (*p >= '0' && *p <= '9') + major = (major * 10) + *p++ - '0'; + if (*p != '.' && *p != '\0') + return -1; + + return kernel * 1000 + major; +} + static inline void init_cpu_features (struct cpu_features *cpu_features) { @@ -126,6 +162,10 @@ init_cpu_features (struct cpu_features *cpu_features) /* Check if SVE is supported. */ cpu_features->sve = GLRO (dl_hwcap) & HWCAP_SVE; + /* Prefer using SVE in string ifuncs from Linux 6.2 onwards. */ + cpu_features->prefer_sve_ifuncs = + cpu_features->sve && kernel_version () >= 6002; + /* Check if MOPS is supported. */ cpu_features->mops = GLRO (dl_hwcap2) & HWCAP2_MOPS; }