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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>
233 lines
4.7 KiB
C
233 lines
4.7 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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#include "vdso.h"
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#include <linux/compiler.h>
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#include <linux/irqchip/mips-gic.h>
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#include <linux/time.h>
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#include <asm/clocksource.h>
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#include <asm/io.h>
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#include <asm/mips-cm.h>
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#include <asm/unistd.h>
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#include <asm/vdso.h>
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static __always_inline int do_realtime_coarse(struct timespec *ts,
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const union mips_vdso_data *data)
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{
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u32 start_seq;
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do {
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start_seq = vdso_data_read_begin(data);
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ts->tv_sec = data->xtime_sec;
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ts->tv_nsec = data->xtime_nsec >> data->cs_shift;
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} while (vdso_data_read_retry(data, start_seq));
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return 0;
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}
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static __always_inline int do_monotonic_coarse(struct timespec *ts,
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const union mips_vdso_data *data)
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{
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u32 start_seq;
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u32 to_mono_sec;
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u32 to_mono_nsec;
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do {
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start_seq = vdso_data_read_begin(data);
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ts->tv_sec = data->xtime_sec;
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ts->tv_nsec = data->xtime_nsec >> data->cs_shift;
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to_mono_sec = data->wall_to_mono_sec;
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to_mono_nsec = data->wall_to_mono_nsec;
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} while (vdso_data_read_retry(data, start_seq));
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ts->tv_sec += to_mono_sec;
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timespec_add_ns(ts, to_mono_nsec);
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return 0;
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}
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#ifdef CONFIG_CSRC_R4K
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static __always_inline u64 read_r4k_count(void)
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{
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unsigned int count;
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__asm__ __volatile__(
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" .set push\n"
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" .set mips32r2\n"
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" rdhwr %0, $2\n"
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" .set pop\n"
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: "=r" (count));
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return count;
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}
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#endif
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#ifdef CONFIG_CLKSRC_MIPS_GIC
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static __always_inline u64 read_gic_count(const union mips_vdso_data *data)
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{
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void __iomem *gic = get_gic(data);
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u32 hi, hi2, lo;
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do {
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hi = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS);
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lo = __raw_readl(gic + GIC_UMV_SH_COUNTER_31_00_OFS);
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hi2 = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS);
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} while (hi2 != hi);
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return (((u64)hi) << 32) + lo;
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}
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#endif
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static __always_inline u64 get_ns(const union mips_vdso_data *data)
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{
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u64 cycle_now, delta, nsec;
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switch (data->clock_mode) {
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#ifdef CONFIG_CSRC_R4K
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case VDSO_CLOCK_R4K:
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cycle_now = read_r4k_count();
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break;
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#endif
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#ifdef CONFIG_CLKSRC_MIPS_GIC
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case VDSO_CLOCK_GIC:
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cycle_now = read_gic_count(data);
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break;
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#endif
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default:
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return 0;
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}
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delta = (cycle_now - data->cs_cycle_last) & data->cs_mask;
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nsec = (delta * data->cs_mult) + data->xtime_nsec;
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nsec >>= data->cs_shift;
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return nsec;
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}
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static __always_inline int do_realtime(struct timespec *ts,
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const union mips_vdso_data *data)
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{
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u32 start_seq;
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u64 ns;
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do {
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start_seq = vdso_data_read_begin(data);
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if (data->clock_mode == VDSO_CLOCK_NONE)
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return -ENOSYS;
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ts->tv_sec = data->xtime_sec;
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ns = get_ns(data);
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} while (vdso_data_read_retry(data, start_seq));
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ts->tv_nsec = 0;
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timespec_add_ns(ts, ns);
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return 0;
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}
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static __always_inline int do_monotonic(struct timespec *ts,
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const union mips_vdso_data *data)
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{
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u32 start_seq;
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u64 ns;
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u32 to_mono_sec;
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u32 to_mono_nsec;
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do {
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start_seq = vdso_data_read_begin(data);
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if (data->clock_mode == VDSO_CLOCK_NONE)
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return -ENOSYS;
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ts->tv_sec = data->xtime_sec;
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ns = get_ns(data);
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to_mono_sec = data->wall_to_mono_sec;
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to_mono_nsec = data->wall_to_mono_nsec;
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} while (vdso_data_read_retry(data, start_seq));
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ts->tv_sec += to_mono_sec;
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ts->tv_nsec = 0;
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timespec_add_ns(ts, ns + to_mono_nsec);
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return 0;
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}
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#ifdef CONFIG_MIPS_CLOCK_VSYSCALL
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/*
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* This is behind the ifdef so that we don't provide the symbol when there's no
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* possibility of there being a usable clocksource, because there's nothing we
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* can do without it. When libc fails the symbol lookup it should fall back on
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* the standard syscall path.
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*/
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int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
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{
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const union mips_vdso_data *data = get_vdso_data();
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struct timespec ts;
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int ret;
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ret = do_realtime(&ts, data);
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if (ret)
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return ret;
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if (tv) {
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tv->tv_sec = ts.tv_sec;
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tv->tv_usec = ts.tv_nsec / 1000;
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}
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if (tz) {
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tz->tz_minuteswest = data->tz_minuteswest;
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tz->tz_dsttime = data->tz_dsttime;
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}
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return 0;
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}
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#endif /* CONFIG_CLKSRC_MIPS_GIC */
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int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
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{
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const union mips_vdso_data *data = get_vdso_data();
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int ret;
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switch (clkid) {
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case CLOCK_REALTIME_COARSE:
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ret = do_realtime_coarse(ts, data);
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break;
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case CLOCK_MONOTONIC_COARSE:
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ret = do_monotonic_coarse(ts, data);
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break;
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case CLOCK_REALTIME:
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ret = do_realtime(ts, data);
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break;
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case CLOCK_MONOTONIC:
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ret = do_monotonic(ts, data);
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break;
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default:
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ret = -ENOSYS;
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break;
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}
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/* If we return -ENOSYS libc should fall back to a syscall. */
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return ret;
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}
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