bcc4a62a73
After reading do_hres() and do_course() and scratching my head a bit, I figured out why the arithmetic is strange. Document it. Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/f66f53d81150bbad47d7b282c9207a71a3ce1c16.1538689401.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
120 lines
2.5 KiB
C
120 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_VGTOD_H
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#define _ASM_X86_VGTOD_H
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#include <linux/compiler.h>
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#include <linux/clocksource.h>
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#include <uapi/linux/time.h>
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#ifdef BUILD_VDSO32_64
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typedef u64 gtod_long_t;
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#else
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typedef unsigned long gtod_long_t;
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#endif
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/*
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* There is one of these objects in the vvar page for each
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* vDSO-accelerated clockid. For high-resolution clocks, this encodes
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* the time corresponding to vsyscall_gtod_data.cycle_last. For coarse
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* clocks, this encodes the actual time.
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*
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* To confuse the reader, for high-resolution clocks, nsec is left-shifted
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* by vsyscall_gtod_data.shift.
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*/
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struct vgtod_ts {
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u64 sec;
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u64 nsec;
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};
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#define VGTOD_BASES (CLOCK_TAI + 1)
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#define VGTOD_HRES (BIT(CLOCK_REALTIME) | BIT(CLOCK_MONOTONIC) | BIT(CLOCK_TAI))
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#define VGTOD_COARSE (BIT(CLOCK_REALTIME_COARSE) | BIT(CLOCK_MONOTONIC_COARSE))
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/*
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* vsyscall_gtod_data will be accessed by 32 and 64 bit code at the same time
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* so be carefull by modifying this structure.
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*/
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struct vsyscall_gtod_data {
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unsigned int seq;
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int vclock_mode;
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u64 cycle_last;
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u64 mask;
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u32 mult;
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u32 shift;
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struct vgtod_ts basetime[VGTOD_BASES];
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int tz_minuteswest;
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int tz_dsttime;
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};
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extern struct vsyscall_gtod_data vsyscall_gtod_data;
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extern int vclocks_used;
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static inline bool vclock_was_used(int vclock)
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{
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return READ_ONCE(vclocks_used) & (1 << vclock);
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}
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static inline unsigned int gtod_read_begin(const struct vsyscall_gtod_data *s)
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{
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unsigned int ret;
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repeat:
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ret = READ_ONCE(s->seq);
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if (unlikely(ret & 1)) {
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cpu_relax();
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goto repeat;
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}
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smp_rmb();
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return ret;
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}
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static inline int gtod_read_retry(const struct vsyscall_gtod_data *s,
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unsigned int start)
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{
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smp_rmb();
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return unlikely(s->seq != start);
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}
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static inline void gtod_write_begin(struct vsyscall_gtod_data *s)
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{
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++s->seq;
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smp_wmb();
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}
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static inline void gtod_write_end(struct vsyscall_gtod_data *s)
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{
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smp_wmb();
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++s->seq;
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}
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#ifdef CONFIG_X86_64
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#define VGETCPU_CPU_MASK 0xfff
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static inline unsigned int __getcpu(void)
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{
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unsigned int p;
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/*
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* Load per CPU data from GDT. LSL is faster than RDTSCP and
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* works on all CPUs. This is volatile so that it orders
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* correctly wrt barrier() and to keep gcc from cleverly
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* hoisting it out of the calling function.
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*
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* If RDPID is available, use it.
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*/
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alternative_io ("lsl %[seg],%[p]",
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".byte 0xf3,0x0f,0xc7,0xf8", /* RDPID %eax/rax */
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X86_FEATURE_RDPID,
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[p] "=a" (p), [seg] "r" (__PER_CPU_SEG));
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return p;
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}
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#endif /* CONFIG_X86_64 */
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#endif /* _ASM_X86_VGTOD_H */
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