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 <maimon.sagi@xxxxxxxxx>
---
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
