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42874e4e |
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08-Nov-2023 |
Arnd Bergmann <arnd@arndb.de> |
arch: vdso: consolidate gettime prototypes The VDSO functions are defined as globals in the kernel sources but intended to be called from userspace, so there is no need to declare them in a kernel side header. Without a prototype, this now causes warnings such as arch/mips/vdso/vgettimeofday.c:14:5: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes] arch/mips/vdso/vgettimeofday.c:28:5: error: no previous prototype for '__vdso_gettimeofday' [-Werror=missing-prototypes] arch/mips/vdso/vgettimeofday.c:36:5: error: no previous prototype for '__vdso_clock_getres' [-Werror=missing-prototypes] arch/mips/vdso/vgettimeofday.c:42:5: error: no previous prototype for '__vdso_clock_gettime64' [-Werror=missing-prototypes] arch/sparc/vdso/vclock_gettime.c:254:1: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes] arch/sparc/vdso/vclock_gettime.c:282:1: error: no previous prototype for '__vdso_clock_gettime_stick' [-Werror=missing-prototypes] arch/sparc/vdso/vclock_gettime.c:307:1: error: no previous prototype for '__vdso_gettimeofday' [-Werror=missing-prototypes] arch/sparc/vdso/vclock_gettime.c:343:1: error: no previous prototype for '__vdso_gettimeofday_stick' [-Werror=missing-prototypes] Most architectures have already added workarounds for these by adding declarations somewhere, but since these are all compatible, we should really just have one copy, with an #ifdef check for the 32-bit vs 64-bit variant and use that everywhere. Unfortunately, the sparc an um versions are currently incompatible since they never added support for __vdso_clock_gettime64() in 32-bit userland. For the moment, I'm leaving this one out, as I can't easily test it and it requires a larger rework. Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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ad5d1122 |
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09-Jun-2020 |
Vincent Chen <vincent.chen@sifive.com> |
riscv: use vDSO common flow to reduce the latency of the time-related functions Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
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