mirror of
https://github.com/torvalds/linux.git
synced 2024-12-23 11:21:33 +00:00
a7f4df4e21
Add user-mode implementations of gettimeofday() and clock_gettime() to
the VDSO. This is currently usable with 2 clocksources: the CP0 count
register, which is accessible to user-mode via RDHWR on R2 and later
cores, or the MIPS Global Interrupt Controller (GIC) timer, which
provides a "user-mode visible" section containing a mirror of its
counter registers. This section must be mapped into user memory, which
is done below the VDSO data page.
When a supported clocksource is not in use, the VDSO functions will
return -ENOSYS, which causes libc to fall back on the standard syscall
path.
When support for neither of these clocksources is compiled into the
kernel at all, the VDSO still provides clock_gettime(), as the coarse
realtime/monotonic clocks can still be implemented. However,
gettimeofday() is not provided in this case as nothing can be done
without a suitable clocksource. This causes the symbol lookup to fail
in libc and it will then always use the standard syscall path.
This patch includes a workaround for a bug in QEMU which results in
RDHWR on the CP0 count register always returning a constant (incorrect)
value. A fix for this has been submitted, and the workaround can be
removed after the fix has been in stable releases for a reasonable
amount of time.
A simple performance test which calls gettimeofday() 1000 times in a
loop and calculates the average execution time gives the following
results on a Malta + I6400 (running at 20MHz):
- Syscall: ~31000 ns
- VDSO (GIC): ~15000 ns
- VDSO (CP0): ~9500 ns
[markos.chandras@imgtec.com:
- Minor code re-arrangements in order for mappings to be made
in the order they appear to the process' address space.
- Move do_{monotonic, realtime} outside of the MIPS_CLOCK_VSYSCALL ifdef
- Use gic_get_usm_range so we can do the GIC mapping in the
arch/mips/kernel/vdso instead of the GIC irqchip driver]
Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11338/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
30 lines
884 B
C
30 lines
884 B
C
/*
|
|
* Copyright (C) 2015 Imagination Technologies
|
|
* Author: Alex Smith <alex.smith@imgtec.com>
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify it
|
|
* under the terms of the GNU General Public License as published by the
|
|
* Free Software Foundation; either version 2 of the License, or (at your
|
|
* option) any later version.
|
|
*/
|
|
|
|
#ifndef __ASM_CLOCKSOURCE_H
|
|
#define __ASM_CLOCKSOURCE_H
|
|
|
|
#include <linux/types.h>
|
|
|
|
/* VDSO clocksources. */
|
|
#define VDSO_CLOCK_NONE 0 /* No suitable clocksource. */
|
|
#define VDSO_CLOCK_R4K 1 /* Use the coprocessor 0 count. */
|
|
#define VDSO_CLOCK_GIC 2 /* Use the GIC. */
|
|
|
|
/**
|
|
* struct arch_clocksource_data - Architecture-specific clocksource information.
|
|
* @vdso_clock_mode: Method the VDSO should use to access the clocksource.
|
|
*/
|
|
struct arch_clocksource_data {
|
|
u8 vdso_clock_mode;
|
|
};
|
|
|
|
#endif /* __ASM_CLOCKSOURCE_H */
|