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| author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2019-12-16 13:50:57 -0300 |
|---|---|---|
| committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2020-01-03 11:22:07 -0300 |
| commit | 92b963699aae2da1e25f47edc7a0408bf3aee4d2 (patch) | |
| tree | ddd0d6395031f782246254f4ec643f9e68dbe46f | |
| parent | 0dc1a378b135ec46fcc451d96c4a3a64c08e2ace (diff) | |
| download | glibc-92b963699aae2da1e25f47edc7a0408bf3aee4d2.tar.gz | |
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 <siddhesh@sourceware.org>
| -rw-r--r-- | sysdeps/unix/sysv/linux/clock_getres.c | 16 |
1 files 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; |