[PATCH v4] posix-timers: add multi_clock_gettime system call
From: Sagi Maimon <hidden>
Date: 2023-12-31 17:07:30
Also in:
linux-arch, lkml, netdev
Subsystem:
abi/api, generic include/asm header files, posix clocks and timers, the rest, x86 architecture (32-bit and 64-bit), x86 entry code · Maintainers:
Arnd Bergmann, Anna-Maria Behnsen, Frederic Weisbecker, Thomas Gleixner, Linus Torvalds, Ingo Molnar, Borislav Petkov, Dave Hansen, Andy Lutomirski
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 <redacted> --- Addressed comments from: - Arnd Bergmann : https://www.spinics.net/lists/netdev/msg962019.html Changes since version 3: - Replacing the clkid fixed size arrays with a dynamically sized array. - Coping only necessary data from user space. - Calling put_timespec64() only after all time samples taken in order to reduce the put_timespec64() overhead. 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 | 59 ++++++++++++++++++++++++++ 5 files changed, 85 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..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