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Re: [PATCH 2/6] linux: Assume clock_getres CLOCK_{PROCESS,THREAD}_CPUTIME_ID
On 11/02/2019 11:22, Carlos O'Donell wrote:
> On 2/11/19 7:54 AM, Florian Weimer wrote:
>> * Adhemerval Zanella:
>>
>>> On 11/02/2019 09:43, Florian Weimer wrote:
>>>> * Adhemerval Zanella:
>>>>
>>>>> nscd uses _SC_MONOTONIC_CLOCK and if I understood correctly both IA64
>>>>> manual and kernel code, the CLOCK_MONOTONIC implementation on SMP IA64
>>>>> system with ITC that may drift is a best effort...
>>>>
>>>> Are you sure about that? Wouldn't that be a bug in kernel
>>>> clock_gettime, and not something we should paper over in userspace?
>>>
>>> Not sure, I was just my impression checking kernel ia64 code but I am
>>> not an architecture expert. To be safe I kept the original code in
>>> patch proposal.
>>
>> I think it's not worth maintaing the ia64 divergence for this. If it is
>> a problem with the kernel's CLOCK_MONOTONIC implementation, it has to be
>> fixed there.
>
> I tend to agree. Standard interfaces should behave in standard ways.
>
> We have the same problem in HPPA where a similar clock (and my feeling was
> always that IA64 derived a lot from HP PARISC 64-bit) that needs synchronization
> at SMP rendevous at boot time, followed by bias and drift adjustment.
>
> For HPPA we made sue that the everything was accurately compensated at the
> kernel timer source level, and never in userspace. You *can* do it in userspace
> and it's faster and lower latency, and all of those things, but it's more complex
> and prone to breakage for odd reasons (compiler optimizations etc.).
>
> For HPPA you can access the tick counter in userspace, raw, and it's
> useful for timing small sequences of code, but if you move to a new CPU
> mid-measurement, you'll get wrong values because the value and bias is per-cpu.
>
Simplified patch below. I decided to keep the syscall issue so kernel can
correctly report its supports.
* sysdeps/unix/sysv/linux/ia64/has_cpuclock.c: Remove file.
* sysdeps/unix/sysv/linux/ia64/sysconf.c: Likewise.
* sysdeps/unix/sysv/linux/sysconf.c (has_cpuclock): Remove function.
(check_clock_getres): New function.
(__sysconf): Use check_clock_getres instead of has_cpuclock.
---
sysdeps/unix/sysv/linux/ia64/has_cpuclock.c | 51 ---------------------
sysdeps/unix/sysv/linux/ia64/sysconf.c | 30 ------------
sysdeps/unix/sysv/linux/sysconf.c | 45 +++++-------------
3 files changed, 11 insertions(+), 115 deletions(-)
delete mode 100644 sysdeps/unix/sysv/linux/ia64/has_cpuclock.c
delete mode 100644 sysdeps/unix/sysv/linux/ia64/sysconf.c
diff --git a/sysdeps/unix/sysv/linux/ia64/has_cpuclock.c b/sysdeps/unix/sysv/linux/ia64/has_cpuclock.c
deleted file mode 100644
index b3afb37f8b..0000000000
--- a/sysdeps/unix/sysv/linux/ia64/has_cpuclock.c
+++ /dev/null
@@ -1,51 +0,0 @@
-/* Copyright (C) 2000-2019 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
-
-#include <errno.h>
-#include <fcntl.h>
-#include <unistd.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <not-cancel.h>
-
-static int itc_usable;
-
-static int
-has_cpuclock (void)
-{
- if (__builtin_expect (itc_usable == 0, 0))
- {
- int newval = 1;
- int fd = __open_nocancel ("/proc/sal/itc_drift", O_RDONLY);
- if (__builtin_expect (fd != -1, 1))
- {
- char buf[16];
- /* We expect the file to contain a single digit followed by
- a newline. If the format changes we better not rely on
- the file content. */
- if (__read_nocancel (fd, buf, sizeof buf) != 2
- || buf[0] != '0' || buf[1] != '\n')
- newval = -1;
-
- __close_nocancel_nostatus (fd);
- }
-
- itc_usable = newval;
- }
-
- return itc_usable;
-}
diff --git a/sysdeps/unix/sysv/linux/ia64/sysconf.c b/sysdeps/unix/sysv/linux/ia64/sysconf.c
deleted file mode 100644
index ef75322f1f..0000000000
--- a/sysdeps/unix/sysv/linux/ia64/sysconf.c
+++ /dev/null
@@ -1,30 +0,0 @@
-/* Get file-specific information about a file. Linux/ia64 version.
- Copyright (C) 2003-2019 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
-
-#include <assert.h>
-#include <stdbool.h>
-#include <stdlib.h>
-#include <unistd.h>
-
-
-#include "has_cpuclock.c"
-#define HAS_CPUCLOCK(name) (has_cpuclock () ? _POSIX_VERSION : -1)
-
-
-/* Now the generic Linux version. */
-#include <sysdeps/unix/sysv/linux/sysconf.c>
diff --git a/sysdeps/unix/sysv/linux/sysconf.c b/sysdeps/unix/sysv/linux/sysconf.c
index 4b297ba35f..55b75190d0 100644
--- a/sysdeps/unix/sysv/linux/sysconf.c
+++ b/sysdeps/unix/sysv/linux/sysconf.c
@@ -35,33 +35,16 @@
static long int posix_sysconf (int name);
-#ifndef HAS_CPUCLOCK
static long int
-has_cpuclock (int name)
+check_clock_getres (clockid_t clk_id)
{
-# if defined __NR_clock_getres || HP_TIMING_AVAIL
- /* If we have HP_TIMING, we will fall back on that if the system
- call does not work, so we support it either way. */
-# if !HP_TIMING_AVAIL
- /* Check using the clock_getres system call. */
struct timespec ts;
INTERNAL_SYSCALL_DECL (err);
- int r = INTERNAL_SYSCALL (clock_getres, err, 2,
- (name == _SC_CPUTIME
- ? CLOCK_PROCESS_CPUTIME_ID
- : CLOCK_THREAD_CPUTIME_ID),
- &ts);
+ int r = INTERNAL_SYSCALL_CALL (clock_getres, err, clk_id, &ts);
if (INTERNAL_SYSCALL_ERROR_P (r, err))
return -1;
-# endif
return _POSIX_VERSION;
-# else
- return -1;
-# endif
}
-# define HAS_CPUCLOCK(name) has_cpuclock (name)
-#endif
-
/* Get the value of the system variable NAME. */
long int
@@ -71,29 +54,22 @@ __sysconf (int name)
switch (name)
{
- struct rlimit rlimit;
-#ifdef __NR_clock_getres
case _SC_MONOTONIC_CLOCK:
- /* Check using the clock_getres system call. */
- {
- struct timespec ts;
- INTERNAL_SYSCALL_DECL (err);
- int r;
- r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
- return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : _POSIX_VERSION;
- }
-#endif
+ return check_clock_getres (CLOCK_MONOTONIC);
case _SC_CPUTIME:
+ return check_clock_getres (CLOCK_PROCESS_CPUTIME_ID);
case _SC_THREAD_CPUTIME:
- return HAS_CPUCLOCK (name);
+ return check_clock_getres (CLOCK_THREAD_CPUTIME_ID);
- case _SC_ARG_MAX:
+ case _SC_ARG_MAX: {
+ struct rlimit rlimit;
/* Use getrlimit to get the stack limit. */
if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
return MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
return legacy_ARG_MAX;
+ } break;
case _SC_NGROUPS_MAX:
/* Try to read the information from the /proc/sys/kernel/ngroups_max
@@ -101,13 +77,14 @@ __sysconf (int name)
procfname = "/proc/sys/kernel/ngroups_max";
break;
- case _SC_SIGQUEUE_MAX:
+ case _SC_SIGQUEUE_MAX: {
+ struct rlimit rlimit;
if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
return rlimit.rlim_cur;
/* The /proc/sys/kernel/rtsig-max file contains the answer. */
procfname = "/proc/sys/kernel/rtsig-max";
- break;
+ } break;
default:
break;
--
2.17.1