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> --- Addressed comments from: - Thomas Gleixner : https://www.spinics.net/lists/netdev/msg959514.html Changes since version 2: - Change multi PHC syscall to fit the Y2038 safe variant. - Define the syscall data structure under uapi directory, so it will be known in user space. arch/x86/entry/syscalls/syscall_64.tbl | 1 + include/linux/syscalls.h | 2 +- include/uapi/asm-generic/unistd.h | 4 +++- include/uapi/linux/multi_clock.h | 21 ++++++++++++++++ kernel/time/posix-timers.c | 33 ++++++++++++++++++++++++++ 5 files changed, 59 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..b59fa776ab76 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -1161,7 +1161,7 @@ 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..07099045ec32 --- /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 5 /* Max number of clocks */ +#define MULTI_PTP_MAX_SAMPLES 10 /* 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..80cbce59d4f4 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -31,6 +31,7 @@ #include <linux/compat.h> #include <linux/nospec.h> #include <linux/time_namespace.h> +#include <linux/multi_clock.h> #include "timekeeping.h" #include "posix-timers.h" @@ -1426,6 +1427,38 @@ 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 __ptp_multi_clock_get multi_clk_get; + unsigned int i, j; + int error; + + if (copy_from_user(&multi_clk_get, ptp_multi_clk_get, sizeof(multi_clk_get))) + return -EFAULT; + + if (multi_clk_get.n_samples > MULTI_PTP_MAX_SAMPLES) + return -EINVAL; + if (multi_clk_get.n_clocks > MULTI_PTP_MAX_CLOCKS) + return -EINVAL; + + for (j = 0; j < multi_clk_get.n_samples; j++) { + for (i = 0; i < multi_clk_get.n_clocks; i++) { + kc = clockid_to_kclock(multi_clk_get.clkid_arr[i]); + if (!kc) + return -EINVAL; + error = kc->clock_get_timespec(multi_clk_get.clkid_arr[i], &kernel_tp); + if (!error && put_timespec64(&kernel_tp, (struct __kernel_timespec __user *) + &ptp_multi_clk_get->ts[j][i])) + error = -EFAULT; + } + } + + 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
