mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-19 02:04:19 +08:00
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>
90 lines
2.1 KiB
C
90 lines
2.1 KiB
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.
|
|
*/
|
|
|
|
#include <asm/sgidefs.h>
|
|
|
|
#if _MIPS_SIM != _MIPS_SIM_ABI64 && defined(CONFIG_64BIT)
|
|
|
|
/* Building 32-bit VDSO for the 64-bit kernel. Fake a 32-bit Kconfig. */
|
|
#undef CONFIG_64BIT
|
|
#define CONFIG_32BIT 1
|
|
#ifndef __ASSEMBLY__
|
|
#include <asm-generic/atomic64.h>
|
|
#endif
|
|
#endif
|
|
|
|
#ifndef __ASSEMBLY__
|
|
|
|
#include <asm/asm.h>
|
|
#include <asm/page.h>
|
|
#include <asm/vdso.h>
|
|
|
|
static inline unsigned long get_vdso_base(void)
|
|
{
|
|
unsigned long addr;
|
|
|
|
/*
|
|
* We can't use cpu_has_mips_r6 since it needs the cpu_data[]
|
|
* kernel symbol.
|
|
*/
|
|
#ifdef CONFIG_CPU_MIPSR6
|
|
/*
|
|
* lapc <symbol> is an alias to addiupc reg, <symbol> - .
|
|
*
|
|
* We can't use addiupc because there is no label-label
|
|
* support for the addiupc reloc
|
|
*/
|
|
__asm__("lapc %0, _start \n"
|
|
: "=r" (addr) : :);
|
|
#else
|
|
/*
|
|
* Get the base load address of the VDSO. We have to avoid generating
|
|
* relocations and references to the GOT because ld.so does not peform
|
|
* relocations on the VDSO. We use the current offset from the VDSO base
|
|
* and perform a PC-relative branch which gives the absolute address in
|
|
* ra, and take the difference. The assembler chokes on
|
|
* "li %0, _start - .", so embed the offset as a word and branch over
|
|
* it.
|
|
*
|
|
*/
|
|
|
|
__asm__(
|
|
" .set push \n"
|
|
" .set noreorder \n"
|
|
" bal 1f \n"
|
|
" nop \n"
|
|
" .word _start - . \n"
|
|
"1: lw %0, 0($31) \n"
|
|
" " STR(PTR_ADDU) " %0, $31, %0 \n"
|
|
" .set pop \n"
|
|
: "=r" (addr)
|
|
:
|
|
: "$31");
|
|
#endif /* CONFIG_CPU_MIPSR6 */
|
|
|
|
return addr;
|
|
}
|
|
|
|
static inline const union mips_vdso_data *get_vdso_data(void)
|
|
{
|
|
return (const union mips_vdso_data *)(get_vdso_base() - PAGE_SIZE);
|
|
}
|
|
|
|
#ifdef CONFIG_CLKSRC_MIPS_GIC
|
|
|
|
static inline void __iomem *get_gic(const union mips_vdso_data *data)
|
|
{
|
|
return (void __iomem *)data - PAGE_SIZE;
|
|
}
|
|
|
|
#endif /* CONFIG_CLKSRC_MIPS_GIC */
|
|
|
|
#endif /* __ASSEMBLY__ */
|