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Message-Id: <20231228122411.3189-1-maimon.sagi@gmail.com>
Date: Thu, 28 Dec 2023 14:24:11 +0200
From: Sagi Maimon <maimon.sagi@...il.com>
To: richardcochran@...il.com,
luto@...nel.org,
datglx@...utronix.de,
mingo@...hat.com,
bp@...en8.de,
dave.hansen@...ux.intel.com,
x86@...nel.org,
hpa@...or.com,
arnd@...db.de,
geert@...ux-m68k.org,
peterz@...radead.org,
hannes@...xchg.org,
sohil.mehta@...el.com,
rick.p.edgecombe@...el.com,
nphamcs@...il.com,
palmer@...ive.com,
maimon.sagi@...il.com,
keescook@...omium.org,
legion@...nel.org,
mark.rutland@....com
Cc: linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org,
linux-arch@...r.kernel.org,
netdev@...r.kernel.org
Subject: [PATCH v3] posix-timers: add multi_clock_gettime system call
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@...il.com>
---
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
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