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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>
137 lines
3.7 KiB
C
137 lines
3.7 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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#ifndef __ASM_VDSO_H
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#define __ASM_VDSO_H
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#include <linux/mm_types.h>
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#include <asm/barrier.h>
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/**
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* struct mips_vdso_image - Details of a VDSO image.
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* @data: Pointer to VDSO image data (page-aligned).
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* @size: Size of the VDSO image data (page-aligned).
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* @off_sigreturn: Offset of the sigreturn() trampoline.
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* @off_rt_sigreturn: Offset of the rt_sigreturn() trampoline.
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* @mapping: Special mapping structure.
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*
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* This structure contains details of a VDSO image, including the image data
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* and offsets of certain symbols required by the kernel. It is generated as
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* part of the VDSO build process, aside from the mapping page array, which is
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* populated at runtime.
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*/
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struct mips_vdso_image {
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void *data;
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unsigned long size;
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unsigned long off_sigreturn;
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unsigned long off_rt_sigreturn;
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struct vm_special_mapping mapping;
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};
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/*
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* The following structures are auto-generated as part of the build for each
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* ABI by genvdso, see arch/mips/vdso/Makefile.
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*/
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extern struct mips_vdso_image vdso_image;
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#ifdef CONFIG_MIPS32_O32
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extern struct mips_vdso_image vdso_image_o32;
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#endif
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#ifdef CONFIG_MIPS32_N32
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extern struct mips_vdso_image vdso_image_n32;
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#endif
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/**
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* union mips_vdso_data - Data provided by the kernel for the VDSO.
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* @xtime_sec: Current real time (seconds part).
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* @xtime_nsec: Current real time (nanoseconds part, shifted).
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* @wall_to_mono_sec: Wall-to-monotonic offset (seconds part).
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* @wall_to_mono_nsec: Wall-to-monotonic offset (nanoseconds part).
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* @seq_count: Counter to synchronise updates (odd = updating).
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* @cs_shift: Clocksource shift value.
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* @clock_mode: Clocksource to use for time functions.
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* @cs_mult: Clocksource multiplier value.
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* @cs_cycle_last: Clock cycle value at last update.
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* @cs_mask: Clocksource mask value.
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* @tz_minuteswest: Minutes west of Greenwich (from timezone).
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* @tz_dsttime: Type of DST correction (from timezone).
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*
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* This structure contains data needed by functions within the VDSO. It is
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* populated by the kernel and mapped read-only into user memory. The time
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* fields are mirrors of internal data from the timekeeping infrastructure.
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*
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* Note: Care should be taken when modifying as the layout must remain the same
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* for both 64- and 32-bit (for 32-bit userland on 64-bit kernel).
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*/
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union mips_vdso_data {
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struct {
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u64 xtime_sec;
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u64 xtime_nsec;
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u32 wall_to_mono_sec;
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u32 wall_to_mono_nsec;
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u32 seq_count;
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u32 cs_shift;
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u8 clock_mode;
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u32 cs_mult;
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u64 cs_cycle_last;
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u64 cs_mask;
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s32 tz_minuteswest;
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s32 tz_dsttime;
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};
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u8 page[PAGE_SIZE];
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};
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static inline u32 vdso_data_read_begin(const union mips_vdso_data *data)
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{
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u32 seq;
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while (true) {
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seq = ACCESS_ONCE(data->seq_count);
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if (likely(!(seq & 1))) {
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/* Paired with smp_wmb() in vdso_data_write_*(). */
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smp_rmb();
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return seq;
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}
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cpu_relax();
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}
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}
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static inline bool vdso_data_read_retry(const union mips_vdso_data *data,
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u32 start_seq)
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{
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/* Paired with smp_wmb() in vdso_data_write_*(). */
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smp_rmb();
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return unlikely(data->seq_count != start_seq);
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}
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static inline void vdso_data_write_begin(union mips_vdso_data *data)
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{
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++data->seq_count;
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/* Ensure sequence update is written before other data page values. */
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smp_wmb();
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}
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static inline void vdso_data_write_end(union mips_vdso_data *data)
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{
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/* Ensure data values are written before updating sequence again. */
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smp_wmb();
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++data->seq_count;
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}
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#endif /* __ASM_VDSO_H */
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