From 92b963699aae2da1e25f47edc7a0408bf3aee4d2 Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Mon, 16 Dec 2019 13:50:57 -0300 Subject: [PATCH] linux: Optimize fallback 32-bit clock_getres This patch avoid probing the __NR_clock_getttime64 syscall each time __clock_gettime64 is issued on a kernel without 64 bit time support. Once ENOSYS is obtained, only 32-bit clock_gettime are used. The following snippet: clock_getres (CLOCK_REALTIME, &(struct timespec) { 0 }); clock_getres (CLOCK_MONOTONIC, &(struct timespec) { 0 }); clock_getres (CLOCK_BOOTTIME, &(struct timespec) { 0 }); clock_getres (20, &(struct timespec) { 0 }); On a kernel without 64 bit time support issues the syscalls: syscall_0x196(0, 0xffb83330, [...]) = -1 ENOSYS (Function not implemented) clock_getres(CLOCK_REALTIME, {tv_sec=0, tv_nsec=1}) = 0 clock_getres(CLOCK_MONOTONIC, {tv_sec=0, tv_nsec=1}) = 0 clock_getres(CLOCK_BOOTTIME, {tv_sec=0, tv_nsec=1}) = 0 Checked on i686-linux-gnu on 4.15 kernel. Reviewed-by: Siddhesh Poyarekar --- sysdeps/unix/sysv/linux/clock_getres.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/sysdeps/unix/sysv/linux/clock_getres.c b/sysdeps/unix/sysv/linux/clock_getres.c index 2ba72110ba..fee693c36f 100644 --- a/sysdeps/unix/sysv/linux/clock_getres.c +++ b/sysdeps/unix/sysv/linux/clock_getres.c @@ -42,13 +42,21 @@ __clock_getres64 (clockid_t clock_id, struct __timespec64 *res) int r; /* Old 32-bit ABI with possible 64-bit time_t support. */ # ifdef __NR_clock_getres_time64 + /* Avoid issue a __NR_clock_getres_time64 syscall on kernels that do not + support 64-bit time_t. */ + static int time64_support = 1; + if (atomic_load_relaxed (&time64_support) != 0) + { # ifdef HAVE_CLOCK_GETRES64_VSYSCALL - r = INLINE_VSYSCALL (clock_getres_time64, 2, clock_id, res); + r = INLINE_VSYSCALL (clock_getres_time64, 2, clock_id, res); # else - r = INLINE_SYSCALL_CALL (clock_getres_time64, clock_id, res); + r = INLINE_SYSCALL_CALL (clock_getres_time64, clock_id, res); # endif - if (r == 0 || errno != ENOSYS) - return r; + if (r == 0 || errno != ENOSYS) + return r; + + atomic_store_relaxed (&time64_support, 0); + } # endif /* Fallback code that uses 32-bit support. */ struct timespec ts32;