This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
[PATCH 16/16] linux: Optimize fallback 32-bit clock_getres
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Tue, 17 Dec 2019 18:47:28 -0300
- Subject: [PATCH 16/16] linux: Optimize fallback 32-bit clock_getres
- References: <20191217214728.2886-1-adhemerval.zanella@linaro.org>
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.
---
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 3d59f11d71..c1e1cf60c6 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) == 1)
+ {
# 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;
--
2.17.1