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| author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2019-12-14 10:05:44 -0300 |
|---|---|---|
| committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2020-01-03 11:22:07 -0300 |
| commit | a9091a12444d551977adb6d8b45b2007881f1b8b (patch) | |
| tree | 6b4de13b241db8e6af35658f1b46fdd075696cd3 | |
| parent | ff500a623d1bf9fb24f30fa80451897b534549e1 (diff) | |
| download | glibc-a9091a12444d551977adb6d8b45b2007881f1b8b.tar.gz | |
linux: Optimize fallback 32-bit clock_gettime
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_gettime (CLOCK_REALTIME, &(struct timespec) { 0 });
clock_gettime (CLOCK_MONOTONIC, &(struct timespec) { 0 });
clock_gettime (CLOCK_BOOTTIME, &(struct timespec) { 0 });
clock_gettime (20, &(struct timespec) { 0 });
On a kernel without 64 bit time support and with vDSO support results
on the following syscalls:
syscall_0x193(0, 0xff87ba30, [...]) = -1 ENOSYS (Function not implemented)
clock_gettime(CLOCK_BOOTTIME, {tv_sec=927082, tv_nsec=474382032}) = 0
clock_gettime(0x14 /* CLOCK_??? */, 0xff87b9f8) = -1 EINVAL (Invalid argument)
While on a kernel without vDSO support:
syscall_0x193(0, 0xbec95550, 0xb6ed2000, 0x1, 0xbec95550, 0) = -1 (errno 38)
clock_gettime(CLOCK_REALTIME, {tv_sec=1576615930, tv_nsec=638250162}) = 0
clock_gettime(CLOCK_MONOTONIC, {tv_sec=1665478, tv_nsec=638779620}) = 0
clock_gettime(CLOCK_BOOTTIME, {tv_sec=1675418, tv_nsec=292932704}) = 0
clock_gettime(0x14 /* CLOCK_??? */, 0xbec95530) = -1 EINVAL (Invalid argument)
Checked on i686-linux-gnu on 4.15 kernel and on a 5.3 kernel.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
| -rw-r--r-- | sysdeps/unix/sysv/linux/clock_gettime.c | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/sysdeps/unix/sysv/linux/clock_gettime.c b/sysdeps/unix/sysv/linux/clock_gettime.c index a530daef1c..d6c0b4f637 100644 --- a/sysdeps/unix/sysv/linux/clock_gettime.c +++ b/sysdeps/unix/sysv/linux/clock_gettime.c @@ -43,13 +43,21 @@ __clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp) int r; /* Old 32-bit ABI with possible 64-bit time_t support. */ # ifdef __NR_clock_gettime64 + /* Avoid issue a __NR_clock_gettime64 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_GETTIME64_VSYSCALL - r = INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp); + r = INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp); # else - r = INLINE_SYSCALL_CALL (clock_gettime64, clock_id, tp); + r = INLINE_SYSCALL_CALL (clock_gettime64, clock_id, tp); # 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 tp32; |