Some user space applications need to read some clocks.
Each read requires moving from user space to kernel space.
The syscall overhead causes unpredictable delay between N clocks reads
Removing this delay causes better synchronization between N clocks.
Introduce a new system call multi_clock_gettime, which can be used to measure
the offset between multiple clocks, from variety of types: PHC, virtual PHC
and various system clocks (CLOCK_REALTIME, CLOCK_MONOTONIC, etc).
The offset includes the total time that the driver needs to read the clock
timestamp.
New system call allows the reading of a list of clocks - up to PTP_MAX_CLOCKS.
Supported clocks IDs: PHC, virtual PHC and various system clocks.
Up to PTP_MAX_SAMPLES times (per clock) in a single system call read.
The system call returns n_clocks timestamps for each measurement:
- clock 0 timestamp
- ...
- clock n timestamp
Signed-off-by: Sagi Maimon <[email protected]>
---
Changes since version 4:
- fix error : 'struct __ptp_multi_clock_get' declared inside parameter list
will not be visible outside of this definition or declaration
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
include/linux/syscalls.h | 3 +-
include/uapi/asm-generic/unistd.h | 4 +-
include/uapi/linux/multi_clock.h | 21 +++++++++
kernel/time/posix-timers.c | 59 ++++++++++++++++++++++++++
5 files changed, 86 insertions(+), 2 deletions(-)
create mode 100644 include/uapi/linux/multi_clock.h
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 8cb8bf68721c..9cdeb0bf49db 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -378,6 +378,7 @@
454 common futex_wake sys_futex_wake
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
+457 common multi_clock_gettime sys_multi_clock_gettime
#
# Due to a historical design error, certain syscalls are numbered differently
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index fd9d12de7e92..bde7dec493fd 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -74,6 +74,7 @@ struct landlock_ruleset_attr;
enum landlock_rule_type;
struct cachestat_range;
struct cachestat;
+struct __ptp_multi_clock_get;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -1161,7 +1162,7 @@ asmlinkage long sys_mmap_pgoff(unsigned long addr, unsigned long len,
unsigned long prot, unsigned long flags,
unsigned long fd, unsigned long pgoff);
asmlinkage long sys_old_mmap(struct mmap_arg_struct __user *arg);
-
+asmlinkage long sys_multi_clock_gettime(struct __ptp_multi_clock_get __user * ptp_multi_clk_get);
/*
* Not a real system call, but a placeholder for syscalls which are
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 756b013fb832..beb3e0052d3c 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -828,9 +828,11 @@ __SYSCALL(__NR_futex_wake, sys_futex_wake)
__SYSCALL(__NR_futex_wait, sys_futex_wait)
#define __NR_futex_requeue 456
__SYSCALL(__NR_futex_requeue, sys_futex_requeue)
+#define __NR_multi_clock_gettime 457
+__SYSCALL(__NR_multi_clock_gettime, sys_multi_clock_gettime)
#undef __NR_syscalls
-#define __NR_syscalls 457
+#define __NR_syscalls 458
/*
* 32 bit systems traditionally used different
diff --git a/include/uapi/linux/multi_clock.h b/include/uapi/linux/multi_clock.h
new file mode 100644
index 000000000000..5e78dac3a533
--- /dev/null
+++ b/include/uapi/linux/multi_clock.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_MULTI_CLOCK_H
+#define _UAPI_MULTI_CLOCK_H
+
+#include <linux/types.h>
+#include <linux/time_types.h>
+
+#define MULTI_PTP_MAX_CLOCKS 32 /* Max number of clocks */
+#define MULTI_PTP_MAX_SAMPLES 32 /* Max allowed offset measurement samples. */
+
+struct __ptp_multi_clock_get {
+ unsigned int n_clocks; /* Desired number of clocks. */
+ unsigned int n_samples; /* Desired number of measurements per clock. */
+ clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
+ /*
+ * Array of list of n_clocks clocks time samples n_samples times.
+ */
+ struct __kernel_timespec ts[MULTI_PTP_MAX_SAMPLES][MULTI_PTP_MAX_CLOCKS];
+};
+
+#endif /* _UAPI_MULTI_CLOCK_H */
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index b924f0f096fa..1d321dc56a25 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -31,6 +31,8 @@
#include <linux/compat.h>
#include <linux/nospec.h>
#include <linux/time_namespace.h>
+#include <linux/multi_clock.h>
+#include <linux/slab.h>
#include "timekeeping.h"
#include "posix-timers.h"
@@ -1426,6 +1428,63 @@ SYSCALL_DEFINE4(clock_nanosleep_time32, clockid_t, which_clock, int, flags,
#endif
+SYSCALL_DEFINE1(multi_clock_gettime, struct __ptp_multi_clock_get __user *, ptp_multi_clk_get)
+{
+ const struct k_clock *kc;
+ struct timespec64 *kernel_tp;
+ struct timespec64 *kernel_tp_base;
+ unsigned int n_clocks; /* Desired number of clocks. */
+ unsigned int n_samples; /* Desired number of measurements per clock. */
+ unsigned int i, j;
+ clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
+ int error = 0;
+
+ if (copy_from_user(&n_clocks, &ptp_multi_clk_get->n_clocks, sizeof(n_clocks)))
+ return -EFAULT;
+ if (copy_from_user(&n_samples, &ptp_multi_clk_get->n_samples, sizeof(n_samples)))
+ return -EFAULT;
+ if (n_samples > MULTI_PTP_MAX_SAMPLES)
+ return -EINVAL;
+ if (n_clocks > MULTI_PTP_MAX_CLOCKS)
+ return -EINVAL;
+ if (copy_from_user(clkid_arr, &ptp_multi_clk_get->clkid_arr,
+ sizeof(clockid_t) * n_clocks))
+ return -EFAULT;
+
+ kernel_tp_base = kmalloc_array(n_clocks * n_samples,
+ sizeof(struct timespec64), GFP_KERNEL);
+ if (!kernel_tp_base)
+ return -ENOMEM;
+
+ kernel_tp = kernel_tp_base;
+ for (j = 0; j < n_samples; j++) {
+ for (i = 0; i < n_clocks; i++) {
+ kc = clockid_to_kclock(clkid_arr[i]);
+ if (!kc) {
+ error = -EINVAL;
+ goto out;
+ }
+ error = kc->clock_get_timespec(clkid_arr[i], kernel_tp++);
+ if (error)
+ goto out;
+ }
+ }
+
+ kernel_tp = kernel_tp_base;
+ for (j = 0; j < n_samples; j++) {
+ for (i = 0; i < n_clocks; i++) {
+ if (put_timespec64(kernel_tp++, (struct __kernel_timespec __user *)
+ &ptp_multi_clk_get->ts[j][i])) {
+ error = -EFAULT;
+ goto out;
+ }
+ }
+ }
+out:
+ kfree(kernel_tp_base);
+ return error;
+}
+
static const struct k_clock clock_realtime = {
.clock_getres = posix_get_hrtimer_res,
.clock_get_timespec = posix_get_realtime_timespec,
--
2.26.3
On Tue, Jan 2, 2024, at 10:18, Sagi Maimon wrote:
> Some user space applications need to read some clocks.
> Each read requires moving from user space to kernel space.
> The syscall overhead causes unpredictable delay between N clocks reads
> Removing this delay causes better synchronization between N clocks.
>
> Introduce a new system call multi_clock_gettime, which can be used to measure
> the offset between multiple clocks, from variety of types: PHC, virtual PHC
> and various system clocks (CLOCK_REALTIME, CLOCK_MONOTONIC, etc).
> The offset includes the total time that the driver needs to read the clock
> timestamp.
>
> New system call allows the reading of a list of clocks - up to PTP_MAX_CLOCKS.
> Supported clocks IDs: PHC, virtual PHC and various system clocks.
> Up to PTP_MAX_SAMPLES times (per clock) in a single system call read.
> The system call returns n_clocks timestamps for each measurement:
> - clock 0 timestamp
> - ...
> - clock n timestamp
>
> Signed-off-by: Sagi Maimon <[email protected]>
> ---
> Changes since version 4:
> - fix error : 'struct __ptp_multi_clock_get' declared inside parameter list
> will not be visible outside of this definition or declaration
I usually put all the changes for previous versions in a
list here, it helps reviewers.
The changes you made for previous versions all look good
to me, but I think there is still a few things worth
considering. I'll also follow up on the earlier threads.
> +#define MULTI_PTP_MAX_CLOCKS 32 /* Max number of clocks */
> +#define MULTI_PTP_MAX_SAMPLES 32 /* Max allowed offset measurement samples. */
> +
> +struct __ptp_multi_clock_get {
> + unsigned int n_clocks; /* Desired number of clocks. */
> + unsigned int n_samples; /* Desired number of measurements per clock. */
> + clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
> + /*
> + * Array of list of n_clocks clocks time samples n_samples times.
> + */
> + struct __kernel_timespec ts[MULTI_PTP_MAX_SAMPLES][MULTI_PTP_MAX_CLOCKS];
> +};
Since you now access each member individually, I think it
makes more sense here to just pass these as four
register arguments. It helps with argument introspection,
avoids a couple of get_user(), and lets you remove the fixed
array dimensions.
> +SYSCALL_DEFINE1(multi_clock_gettime, struct __ptp_multi_clock_get
> __user *, ptp_multi_clk_get)
> +{
> + const struct k_clock *kc;
> + struct timespec64 *kernel_tp;
> + struct timespec64 *kernel_tp_base;
> + unsigned int n_clocks; /* Desired number of clocks. */
> + unsigned int n_samples; /* Desired number of measurements per clock.
> */
> + unsigned int i, j;
> + clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
> + int error = 0;
> +
> + if (copy_from_user(&n_clocks, &ptp_multi_clk_get->n_clocks,
> sizeof(n_clocks)))
> + return -EFAULT;
> + if (copy_from_user(&n_samples, &ptp_multi_clk_get->n_samples,
> sizeof(n_samples)))
If these remain as struct members rather than register arguments,
you should use get_user() instead of copy_from_user().
> + kernel_tp_base = kmalloc_array(n_clocks * n_samples,
> + sizeof(struct timespec64), GFP_KERNEL);
> + if (!kernel_tp_base)
> + return -ENOMEM;
To be on the safe side regarding possible data leak, maybe use
kcalloc() instead of kmalloc_array() here.
> + kernel_tp = kernel_tp_base;
> + for (j = 0; j < n_samples; j++) {
> + for (i = 0; i < n_clocks; i++) {
> + if (put_timespec64(kernel_tp++, (struct __kernel_timespec __user *)
> + &ptp_multi_clk_get->ts[j][i])) {
I think the typecast here can be removed.
Arnd
On Tue, Jan 2, 2024 at 12:22 PM Arnd Bergmann <[email protected]> wrote:
>
> On Tue, Jan 2, 2024, at 10:18, Sagi Maimon wrote:
> > Some user space applications need to read some clocks.
> > Each read requires moving from user space to kernel space.
> > The syscall overhead causes unpredictable delay between N clocks reads
> > Removing this delay causes better synchronization between N clocks.
> >
> > Introduce a new system call multi_clock_gettime, which can be used to measure
> > the offset between multiple clocks, from variety of types: PHC, virtual PHC
> > and various system clocks (CLOCK_REALTIME, CLOCK_MONOTONIC, etc).
> > The offset includes the total time that the driver needs to read the clock
> > timestamp.
> >
> > New system call allows the reading of a list of clocks - up to PTP_MAX_CLOCKS.
> > Supported clocks IDs: PHC, virtual PHC and various system clocks.
> > Up to PTP_MAX_SAMPLES times (per clock) in a single system call read.
> > The system call returns n_clocks timestamps for each measurement:
> > - clock 0 timestamp
> > - ...
> > - clock n timestamp
> >
> > Signed-off-by: Sagi Maimon <[email protected]>
> > ---
> > Changes since version 4:
> > - fix error : 'struct __ptp_multi_clock_get' declared inside parameter list
> > will not be visible outside of this definition or declaration
>
> I usually put all the changes for previous versions in a
> list here, it helps reviewers.
>
Will be done on patch V6.
> The changes you made for previous versions all look good
> to me, but I think there is still a few things worth
> considering. I'll also follow up on the earlier threads.
>
> > +#define MULTI_PTP_MAX_CLOCKS 32 /* Max number of clocks */
> > +#define MULTI_PTP_MAX_SAMPLES 32 /* Max allowed offset measurement samples. */
> > +
> > +struct __ptp_multi_clock_get {
> > + unsigned int n_clocks; /* Desired number of clocks. */
> > + unsigned int n_samples; /* Desired number of measurements per clock. */
> > + clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
> > + /*
> > + * Array of list of n_clocks clocks time samples n_samples times.
> > + */
> > + struct __kernel_timespec ts[MULTI_PTP_MAX_SAMPLES][MULTI_PTP_MAX_CLOCKS];
> > +};
>
> Since you now access each member individually, I think it
> makes more sense here to just pass these as four
> register arguments. It helps with argument introspection,
> avoids a couple of get_user(), and lets you remove the fixed
> array dimensions.
>
I prefer the use of get_user(), I will use it to remove the fixed
array dimensions.
which will be done on patch V6.
> > +SYSCALL_DEFINE1(multi_clock_gettime, struct __ptp_multi_clock_get
> > __user *, ptp_multi_clk_get)
> > +{
> > + const struct k_clock *kc;
> > + struct timespec64 *kernel_tp;
> > + struct timespec64 *kernel_tp_base;
> > + unsigned int n_clocks; /* Desired number of clocks. */
> > + unsigned int n_samples; /* Desired number of measurements per clock.
> > */
> > + unsigned int i, j;
> > + clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
> > + int error = 0;
> > +
> > + if (copy_from_user(&n_clocks, &ptp_multi_clk_get->n_clocks,
> > sizeof(n_clocks)))
> > + return -EFAULT;
> > + if (copy_from_user(&n_samples, &ptp_multi_clk_get->n_samples,
> > sizeof(n_samples)))
>
> If these remain as struct members rather than register arguments,
> you should use get_user() instead of copy_from_user().
>
Will be done on patch V6
> > + kernel_tp_base = kmalloc_array(n_clocks * n_samples,
> > + sizeof(struct timespec64), GFP_KERNEL);
> > + if (!kernel_tp_base)
> > + return -ENOMEM;
>
> To be on the safe side regarding possible data leak, maybe use
> kcalloc() instead of kmalloc_array() here.
>
Will be done on patch V6.
> > + kernel_tp = kernel_tp_base;
> > + for (j = 0; j < n_samples; j++) {
> > + for (i = 0; i < n_clocks; i++) {
> > + if (put_timespec64(kernel_tp++, (struct __kernel_timespec __user *)
> > + &ptp_multi_clk_get->ts[j][i])) {
>
> I think the typecast here can be removed.
>
You are right, will be fixed on patch V6.
> Arnd
Thanks for your Notes.
Hi Sagi,
kernel test robot noticed the following build errors:
[auto build test ERROR on tip/x86/asm]
[also build test ERROR on arnd-asm-generic/master tip/timers/core linus/master v6.7-rc8]
[cannot apply to next-20240103]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Sagi-Maimon/posix-timers-add-multi_clock_gettime-system-call/20240102-172105
base: tip/x86/asm
patch link: https://lore.kernel.org/r/20240102091855.70418-1-maimon.sagi%40gmail.com
patch subject: [PATCH v5] posix-timers: add multi_clock_gettime system call
config: csky-randconfig-002-20240104 (https://download.01.org/0day-ci/archive/20240104/[email protected]/config)
compiler: csky-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240104/[email protected]/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
All errors (new ones prefixed by >>):
>> csky-linux-ld: arch/csky/kernel/syscall_table.o:(.data..page_aligned+0x724): undefined reference to `sys_multi_clock_gettime'
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On Tue, Jan 02 2024 at 11:18, Sagi Maimon wrote:
> Some user space applications need to read some clocks.
> Each read requires moving from user space to kernel space.
> The syscall overhead causes unpredictable delay between N clocks reads
> Removing this delay causes better synchronization between N clocks.
As I explained to you before: This is wishful thinking.
There is absolutely no guarantee that the syscall will yield better
results. It might on average, but that's a useless measure.
You also still fail to explain what this is going to solve and how it's
used.
> Some user space applications need to read some clocks.
Is just not an explanation at all.
Thanks,
tglx