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>
89 lines
2.1 KiB
C
89 lines
2.1 KiB
C
/*
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* Copyright (C) 2015 Imagination Technologies
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* Author: Alex Smith <alex.smith@imgtec.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version.
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*/
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#include <asm/sgidefs.h>
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#if _MIPS_SIM != _MIPS_SIM_ABI64 && defined(CONFIG_64BIT)
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/* Building 32-bit VDSO for the 64-bit kernel. Fake a 32-bit Kconfig. */
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#undef CONFIG_64BIT
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#define CONFIG_32BIT 1
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#ifndef __ASSEMBLY__
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#include <asm-generic/atomic64.h>
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#endif
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#endif
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#ifndef __ASSEMBLY__
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#include <asm/asm.h>
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#include <asm/page.h>
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#include <asm/vdso.h>
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static inline unsigned long get_vdso_base(void)
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{
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unsigned long addr;
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/*
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* We can't use cpu_has_mips_r6 since it needs the cpu_data[]
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* kernel symbol.
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*/
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#ifdef CONFIG_CPU_MIPSR6
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/*
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* lapc <symbol> is an alias to addiupc reg, <symbol> - .
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*
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* We can't use addiupc because there is no label-label
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* support for the addiupc reloc
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*/
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__asm__("lapc %0, _start \n"
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: "=r" (addr) : :);
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#else
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/*
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* Get the base load address of the VDSO. We have to avoid generating
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* relocations and references to the GOT because ld.so does not peform
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* relocations on the VDSO. We use the current offset from the VDSO base
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* and perform a PC-relative branch which gives the absolute address in
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* ra, and take the difference. The assembler chokes on
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* "li %0, _start - .", so embed the offset as a word and branch over
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* it.
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*
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*/
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__asm__(
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" .set push \n"
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" .set noreorder \n"
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" bal 1f \n"
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" nop \n"
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" .word _start - . \n"
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"1: lw %0, 0($31) \n"
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" " STR(PTR_ADDU) " %0, $31, %0 \n"
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" .set pop \n"
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: "=r" (addr)
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:
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: "$31");
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#endif /* CONFIG_CPU_MIPSR6 */
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return addr;
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}
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static inline const union mips_vdso_data *get_vdso_data(void)
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{
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return (const union mips_vdso_data *)(get_vdso_base() - PAGE_SIZE);
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}
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#ifdef CONFIG_CLKSRC_MIPS_GIC
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static inline void __iomem *get_gic(const union mips_vdso_data *data)
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{
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return (void __iomem *)data - PAGE_SIZE;
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}
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#endif /* CONFIG_CLKSRC_MIPS_GIC */
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#endif /* __ASSEMBLY__ */
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