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ed4f20943c
Converting a 64 Bit TOD format value to nanoseconds means that the value must be divided by 4.096. In order to achieve that we multiply with 125 and divide by 512. When used within sched_clock() this triggers an overflow after appr. 417 days. Resulting in a sched_clock() return value that is much smaller than previously and therefore may cause all sort of weird things in subsystems that rely on a monotonic sched_clock() behaviour. To fix this implement a tod_to_ns() helper function which converts TOD values without overflow and call this function from both places that open coded the conversion: sched_clock() and kvm_s390_handle_wait(). Cc: stable@kernel.org Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
160 lines
3.6 KiB
C
160 lines
3.6 KiB
C
/*
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* S390 version
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* Copyright IBM Corp. 1999
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*
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* Derived from "include/asm-i386/timex.h"
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* Copyright (C) 1992, Linus Torvalds
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*/
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#ifndef _ASM_S390_TIMEX_H
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#define _ASM_S390_TIMEX_H
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#include <asm/lowcore.h>
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/* The value of the TOD clock for 1.1.1970. */
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#define TOD_UNIX_EPOCH 0x7d91048bca000000ULL
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/* Inline functions for clock register access. */
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static inline int set_clock(__u64 time)
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{
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int cc;
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asm volatile(
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" sck %1\n"
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" ipm %0\n"
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" srl %0,28\n"
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: "=d" (cc) : "Q" (time) : "cc");
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return cc;
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}
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static inline int store_clock(__u64 *time)
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{
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int cc;
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asm volatile(
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" stck %1\n"
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" ipm %0\n"
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" srl %0,28\n"
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: "=d" (cc), "=Q" (*time) : : "cc");
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return cc;
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}
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static inline void set_clock_comparator(__u64 time)
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{
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asm volatile("sckc %0" : : "Q" (time));
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}
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static inline void store_clock_comparator(__u64 *time)
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{
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asm volatile("stckc %0" : "=Q" (*time));
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}
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void clock_comparator_work(void);
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static inline unsigned long long local_tick_disable(void)
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{
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unsigned long long old;
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old = S390_lowcore.clock_comparator;
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S390_lowcore.clock_comparator = -1ULL;
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set_clock_comparator(S390_lowcore.clock_comparator);
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return old;
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}
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static inline void local_tick_enable(unsigned long long comp)
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{
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S390_lowcore.clock_comparator = comp;
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set_clock_comparator(S390_lowcore.clock_comparator);
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}
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#define CLOCK_TICK_RATE 1193180 /* Underlying HZ */
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typedef unsigned long long cycles_t;
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static inline unsigned long long get_clock(void)
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{
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unsigned long long clk;
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#ifdef CONFIG_HAVE_MARCH_Z9_109_FEATURES
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asm volatile(".insn s,0xb27c0000,%0" : "=Q" (clk) : : "cc");
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#else
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asm volatile("stck %0" : "=Q" (clk) : : "cc");
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#endif
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return clk;
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}
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static inline void get_clock_ext(char *clk)
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{
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asm volatile("stcke %0" : "=Q" (*clk) : : "cc");
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}
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static inline unsigned long long get_clock_xt(void)
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{
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unsigned char clk[16];
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get_clock_ext(clk);
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return *((unsigned long long *)&clk[1]);
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}
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static inline cycles_t get_cycles(void)
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{
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return (cycles_t) get_clock() >> 2;
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}
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int get_sync_clock(unsigned long long *clock);
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void init_cpu_timer(void);
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unsigned long long monotonic_clock(void);
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void tod_to_timeval(__u64, struct timespec *);
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static inline
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void stck_to_timespec(unsigned long long stck, struct timespec *ts)
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{
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tod_to_timeval(stck - TOD_UNIX_EPOCH, ts);
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}
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extern u64 sched_clock_base_cc;
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/**
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* get_clock_monotonic - returns current time in clock rate units
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*
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* The caller must ensure that preemption is disabled.
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* The clock and sched_clock_base get changed via stop_machine.
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* Therefore preemption must be disabled when calling this
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* function, otherwise the returned value is not guaranteed to
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* be monotonic.
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*/
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static inline unsigned long long get_clock_monotonic(void)
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{
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return get_clock_xt() - sched_clock_base_cc;
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}
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/**
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* tod_to_ns - convert a TOD format value to nanoseconds
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* @todval: to be converted TOD format value
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* Returns: number of nanoseconds that correspond to the TOD format value
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*
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* Converting a 64 Bit TOD format value to nanoseconds means that the value
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* must be divided by 4.096. In order to achieve that we multiply with 125
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* and divide by 512:
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*
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* ns = (todval * 125) >> 9;
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*
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* In order to avoid an overflow with the multiplication we can rewrite this.
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* With a split todval == 2^32 * th + tl (th upper 32 bits, tl lower 32 bits)
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* we end up with
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*
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* ns = ((2^32 * th + tl) * 125 ) >> 9;
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* -> ns = (2^23 * th * 125) + ((tl * 125) >> 9);
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*
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*/
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static inline unsigned long long tod_to_ns(unsigned long long todval)
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{
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unsigned long long ns;
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ns = ((todval >> 32) << 23) * 125;
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ns += ((todval & 0xffffffff) * 125) >> 9;
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return ns;
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}
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#endif
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