[PATCH 18/18] linux: Only use 64-bit syscall if required for clock_nanosleep
Lukasz Majewski
lukma@denx.de
Thu Jun 17 15:11:15 GMT 2021
Hi Adhemerval,
> For !__ASSUME_TIME64_SYSCALLS there is no need to issue a 64-bit
> syscall if the provided timeout fits in a 32-bit one. The 64-bit
> usage should be rare since the timeout is a relative one.
I'm not sure if the above description is correct.
As fair as I understand this patch set - we check if timeout fits into
32-bit if:
- We want to use legacy (32 bit) syscall when __ASSUME_TIME64_SYSCALLS
is not defined to avoid calling syscalls twice.
The problem with relative 64 bit timeouts will be apparent after we
pass Y2038 year threshold.
>
> Checked on i686-linux-gnu on a 4.15 kernel and on a 5.11 kernel
> (with and without --enable-kernel=5.1) and on x86_64-linux-gnu.
> ---
> sysdeps/unix/sysv/linux/clock_nanosleep.c | 47
> +++++++++++++---------- time/Makefile |
> 9 +++++ time/tst-clock_nanosleep.c | 40
> +++++++++++-------- 3 files changed, 60 insertions(+), 36 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c
> b/sysdeps/unix/sysv/linux/clock_nanosleep.c index
> 007f1736cb..46b0f1e269 100644 ---
> a/sysdeps/unix/sysv/linux/clock_nanosleep.c +++
> b/sysdeps/unix/sysv/linux/clock_nanosleep.c @@ -27,8 +27,9 @@
> /* We can simply use the syscall. The CPU clocks are not supported
> with this function. */
> int
> -__clock_nanosleep_time64 (clockid_t clock_id, int flags, const
> struct __timespec64 *req,
> - struct __timespec64 *rem)
> +__clock_nanosleep_time64 (clockid_t clock_id, int flags,
> + const struct __timespec64 *req,
> + struct __timespec64 *rem)
> {
> if (clock_id == CLOCK_THREAD_CPUTIME_ID)
> return EINVAL;
> @@ -37,33 +38,37 @@ __clock_nanosleep_time64 (clockid_t clock_id, int
> flags, const struct __timespec
> /* If the call is interrupted by a signal handler or encounters an
> error, it returns a positive value similar to errno. */
> +
> #ifndef __NR_clock_nanosleep_time64
> # define __NR_clock_nanosleep_time64 __NR_clock_nanosleep
> #endif
> - int r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id,
> - flags, req, rem);
> -
> -#ifndef __ASSUME_TIME64_SYSCALLS
> - if (r == 0 || r != -ENOSYS)
> - return -r;
>
> - if (! in_time_t_range (req->tv_sec))
> + int r;
> +#ifdef __ASSUME_TIME64_SYSCALLS
> + r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id,
> flags, req,
> + rem);
> +#else
> + bool is32bit = in_time_t_range (req->tv_sec);
> + if (!is32bit)
> {
> - __set_errno (EOVERFLOW);
> - return -1;
> + r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id,
> flags,
> + req, rem);
> + if (r == -ENOSYS)
> + r = -EOVERFLOW;
> }
> -
> - struct timespec tr32;
> - struct timespec ts32 = valid_timespec64_to_timespec (*req);
> - r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep, clock_id, flags,
> - &ts32, &tr32);
> - if (INTERNAL_SYSCALL_ERROR_P (r))
> + else
> {
> - if (r == -EINTR && rem != NULL && (flags & TIMER_ABSTIME) == 0)
> - *rem = valid_timespec_to_timespec64 (tr32);
> + struct timespec tr32;
> + struct timespec ts32 = valid_timespec64_to_timespec (*req);
> + r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep, clock_id, flags,
> &ts32,
> + &tr32);
> + if (INTERNAL_SYSCALL_ERROR_P (r))
> + {
> + if (r == -EINTR && rem != NULL && (flags & TIMER_ABSTIME)
> == 0)
> + *rem = valid_timespec_to_timespec64 (tr32);
> + }
> }
> -#endif /* __ASSUME_TIME64_SYSCALLS */
> -
> +#endif
> return -r;
> }
>
> diff --git a/time/Makefile b/time/Makefile
> index c84bd5d3ec..0bea84966c 100644
> --- a/time/Makefile
> +++ b/time/Makefile
> @@ -86,6 +86,15 @@ $(objpfx)tst-strftime2.out: $(gen-locales)
> $(objpfx)tst-strftime3.out: $(gen-locales)
> endif
>
> +ifeq (yes,$(build-shared))
> +librt = $(common-objpfx)rt/librt.so
> +else
> +librt = $(common-objpfx)rt/librt.a
> +endif
> +
> +$(objpfx)tst-clock_nanosleep: $(librt)
> +$(objpfx)tst-clock_nanosleep-time64: $(librt)
> +
> tz-cflags = -DTZDIR='"$(zonedir)"' \
> -DTZDEFAULT='"$(localtime-file)"' \
> -DTZDEFRULES='"$(posixrules-file)"'
> diff --git a/time/tst-clock_nanosleep.c b/time/tst-clock_nanosleep.c
> index 47537435c1..a5a7f9430a 100644
> --- a/time/tst-clock_nanosleep.c
> +++ b/time/tst-clock_nanosleep.c
> @@ -20,38 +20,48 @@
> #include <unistd.h>
> #include <sys/time.h>
> #include <time.h>
> -
> +#include <intprops.h>
> +#include <support/support.h>
> +#include <support/check.h>
>
> /* Test that clock_nanosleep() does sleep. */
> -static int
> -do_test (void)
> +static void
> +clock_nanosleep_test (void)
> {
> /* Current time. */
> struct timeval tv1;
> - (void) gettimeofday (&tv1, NULL);
> + gettimeofday (&tv1, NULL);
>
> - struct timespec ts;
> - ts.tv_sec = 1;
> - ts.tv_nsec = 0;
> + struct timespec ts = { 1, 0 };
> TEMP_FAILURE_RETRY (clock_nanosleep (CLOCK_REALTIME, 0, &ts, &ts));
>
> /* At least one second must have passed. */
> struct timeval tv2;
> - (void) gettimeofday (&tv2, NULL);
> + gettimeofday (&tv2, NULL);
>
> tv2.tv_sec -= tv1.tv_sec;
> tv2.tv_usec -= tv1.tv_usec;
> if (tv2.tv_usec < 0)
> --tv2.tv_sec;
>
> - if (tv2.tv_sec < 1)
> - {
> - puts ("clock_nanosleep didn't sleep long enough");
> - return 1;
> - }
> + TEST_VERIFY (tv2.tv_sec >= 1);
> +}
> +
> +static void
> +clock_nanosleep_large_timeout (void)
> +{
Please correct me if I'm wrong:
> + support_create_timer (0, 100000000, false, NULL);
You create timer with 100ms timeout
> + struct timespec ts = { TYPE_MAXIMUM (time_t), 0 };
ts is created to have maximal value for time_t seconds.
> + int r = clock_nanosleep (CLOCK_REALTIME, 0, &ts, NULL);
The clock_nanosleep is called (64 or 32 bit version - with proper
in-glibc aliasing).
> + TEST_VERIFY (r == EINTR || r == EOVERFLOW);
We check if:
- return is EOVERFLOW - this means that we want to use 64 bit time on
machine which is only supporting 64 bit time.
- return is EINTR - as the timer's (introduced in the earlier patch in
this set) alarm triggers. Am I right that this check is to find out
if the syscall is correctly executed by the kernel?
Or is there any other issue?
> +}
>
> +static int
> +do_test (void)
> +{
> + clock_nanosleep_test ();
> + clock_nanosleep_large_timeout ();
> return 0;
> }
>
> -#define TEST_FUNCTION do_test ()
> -#include "../test-skeleton.c"
> +#include <support/test-driver.c>
Best regards,
Lukasz Majewski
--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de
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