From a7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6 Mon Sep 17 00:00:00 2001 From: Alex Smith Date: Wed, 21 Oct 2015 09:57:44 +0100 Subject: MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() 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 Signed-off-by: Markos Chandras 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 --- arch/mips/vdso/gettimeofday.c | 232 ++++++++++++++++++++++++++++++++++++++++++ arch/mips/vdso/vdso.h | 9 ++ arch/mips/vdso/vdso.lds.S | 5 + 3 files changed, 246 insertions(+) create mode 100644 arch/mips/vdso/gettimeofday.c (limited to 'arch/mips/vdso') diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c new file mode 100644 index 000000000000..ce89c9e294f9 --- /dev/null +++ b/arch/mips/vdso/gettimeofday.c @@ -0,0 +1,232 @@ +/* + * Copyright (C) 2015 Imagination Technologies + * Author: Alex Smith + * + * 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 "vdso.h" + +#include +#include +#include + +#include +#include +#include +#include +#include + +static __always_inline int do_realtime_coarse(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + + do { + start_seq = vdso_data_read_begin(data); + + ts->tv_sec = data->xtime_sec; + ts->tv_nsec = data->xtime_nsec >> data->cs_shift; + } while (vdso_data_read_retry(data, start_seq)); + + return 0; +} + +static __always_inline int do_monotonic_coarse(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + u32 to_mono_sec; + u32 to_mono_nsec; + + do { + start_seq = vdso_data_read_begin(data); + + ts->tv_sec = data->xtime_sec; + ts->tv_nsec = data->xtime_nsec >> data->cs_shift; + + to_mono_sec = data->wall_to_mono_sec; + to_mono_nsec = data->wall_to_mono_nsec; + } while (vdso_data_read_retry(data, start_seq)); + + ts->tv_sec += to_mono_sec; + timespec_add_ns(ts, to_mono_nsec); + + return 0; +} + +#ifdef CONFIG_CSRC_R4K + +static __always_inline u64 read_r4k_count(void) +{ + unsigned int count; + + __asm__ __volatile__( + " .set push\n" + " .set mips32r2\n" + " rdhwr %0, $2\n" + " .set pop\n" + : "=r" (count)); + + return count; +} + +#endif + +#ifdef CONFIG_CLKSRC_MIPS_GIC + +static __always_inline u64 read_gic_count(const union mips_vdso_data *data) +{ + void __iomem *gic = get_gic(data); + u32 hi, hi2, lo; + + do { + hi = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS); + lo = __raw_readl(gic + GIC_UMV_SH_COUNTER_31_00_OFS); + hi2 = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS); + } while (hi2 != hi); + + return (((u64)hi) << 32) + lo; +} + +#endif + +static __always_inline u64 get_ns(const union mips_vdso_data *data) +{ + u64 cycle_now, delta, nsec; + + switch (data->clock_mode) { +#ifdef CONFIG_CSRC_R4K + case VDSO_CLOCK_R4K: + cycle_now = read_r4k_count(); + break; +#endif +#ifdef CONFIG_CLKSRC_MIPS_GIC + case VDSO_CLOCK_GIC: + cycle_now = read_gic_count(data); + break; +#endif + default: + return 0; + } + + delta = (cycle_now - data->cs_cycle_last) & data->cs_mask; + + nsec = (delta * data->cs_mult) + data->xtime_nsec; + nsec >>= data->cs_shift; + + return nsec; +} + +static __always_inline int do_realtime(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + u64 ns; + + do { + start_seq = vdso_data_read_begin(data); + + if (data->clock_mode == VDSO_CLOCK_NONE) + return -ENOSYS; + + ts->tv_sec = data->xtime_sec; + ns = get_ns(data); + } while (vdso_data_read_retry(data, start_seq)); + + ts->tv_nsec = 0; + timespec_add_ns(ts, ns); + + return 0; +} + +static __always_inline int do_monotonic(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + u64 ns; + u32 to_mono_sec; + u32 to_mono_nsec; + + do { + start_seq = vdso_data_read_begin(data); + + if (data->clock_mode == VDSO_CLOCK_NONE) + return -ENOSYS; + + ts->tv_sec = data->xtime_sec; + ns = get_ns(data); + + to_mono_sec = data->wall_to_mono_sec; + to_mono_nsec = data->wall_to_mono_nsec; + } while (vdso_data_read_retry(data, start_seq)); + + ts->tv_sec += to_mono_sec; + ts->tv_nsec = 0; + timespec_add_ns(ts, ns + to_mono_nsec); + + return 0; +} + +#ifdef CONFIG_MIPS_CLOCK_VSYSCALL + +/* + * This is behind the ifdef so that we don't provide the symbol when there's no + * possibility of there being a usable clocksource, because there's nothing we + * can do without it. When libc fails the symbol lookup it should fall back on + * the standard syscall path. + */ +int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz) +{ + const union mips_vdso_data *data = get_vdso_data(); + struct timespec ts; + int ret; + + ret = do_realtime(&ts, data); + if (ret) + return ret; + + if (tv) { + tv->tv_sec = ts.tv_sec; + tv->tv_usec = ts.tv_nsec / 1000; + } + + if (tz) { + tz->tz_minuteswest = data->tz_minuteswest; + tz->tz_dsttime = data->tz_dsttime; + } + + return 0; +} + +#endif /* CONFIG_CLKSRC_MIPS_GIC */ + +int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts) +{ + const union mips_vdso_data *data = get_vdso_data(); + int ret; + + switch (clkid) { + case CLOCK_REALTIME_COARSE: + ret = do_realtime_coarse(ts, data); + break; + case CLOCK_MONOTONIC_COARSE: + ret = do_monotonic_coarse(ts, data); + break; + case CLOCK_REALTIME: + ret = do_realtime(ts, data); + break; + case CLOCK_MONOTONIC: + ret = do_monotonic(ts, data); + break; + default: + ret = -ENOSYS; + break; + } + + /* If we return -ENOSYS libc should fall back to a syscall. */ + return ret; +} diff --git a/arch/mips/vdso/vdso.h b/arch/mips/vdso/vdso.h index 0bb6b1adc385..cfb1be441dec 100644 --- a/arch/mips/vdso/vdso.h +++ b/arch/mips/vdso/vdso.h @@ -77,4 +77,13 @@ 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__ */ diff --git a/arch/mips/vdso/vdso.lds.S b/arch/mips/vdso/vdso.lds.S index 21655b6fefc5..8df7dd53e8e0 100644 --- a/arch/mips/vdso/vdso.lds.S +++ b/arch/mips/vdso/vdso.lds.S @@ -95,6 +95,11 @@ PHDRS VERSION { LINUX_2.6 { +#ifndef DISABLE_MIPS_VDSO + global: + __vdso_clock_gettime; + __vdso_gettimeofday; +#endif local: *; }; } -- cgit v1.2.3