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/*
* sched_clock.h: support for extending counters to full 64-bit ns counter
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#ifndef ASM_SCHED_CLOCK
#define ASM_SCHED_CLOCK
#include <linux/kernel.h>
#include <linux/types.h>
struct clock_data {
u64 epoch_ns;
u32 epoch_cyc;
u32 epoch_cyc_copy;
u32 mult;
u32 shift;
};
#define DEFINE_CLOCK_DATA(name) struct clock_data name
static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
return (cyc * mult) >> shift;
}
/*
* Atomically update the sched_clock epoch. Your update callback will
* be called from a timer before the counter wraps - read the current
* counter value, and call this function to safely move the epochs
* forward. Only use this from the update callback.
*/
static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
{
unsigned long flags;
u64 ns = cd->epoch_ns +
cyc_to_ns((cyc - cd->epoch_cyc) & mask, cd->mult, cd->shift);
/*
* Write epoch_cyc and epoch_ns in a way that the update is
* detectable in cyc_to_fixed_sched_clock().
*/
raw_local_irq_save(flags);
cd->epoch_cyc = cyc;
smp_wmb();
cd->epoch_ns = ns;
smp_wmb();
cd->epoch_cyc_copy = cyc;
raw_local_irq_restore(flags);
}
/*
* If your clock rate is known at compile time, using this will allow
* you to optimize the mult/shift loads away. This is paired with
* init_fixed_sched_clock() to ensure that your mult/shift are correct.
*/
static inline unsigned long long cyc_to_fixed_sched_clock(struct clock_data *cd,
u32 cyc, u32 mask, u32 mult, u32 shift)
{
u64 epoch_ns;
u32 epoch_cyc;
/*
* Load the epoch_cyc and epoch_ns atomically. We do this by
* ensuring that we always write epoch_cyc, epoch_ns and
* epoch_cyc_copy in strict order, and read them in strict order.
* If epoch_cyc and epoch_cyc_copy are not equal, then we're in
* the middle of an update, and we should repeat the load.
*/
do {
epoch_cyc = cd->epoch_cyc;
smp_rmb();
epoch_ns = cd->epoch_ns;
smp_rmb();
} while (epoch_cyc != cd->epoch_cyc_copy);
return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, mult, shift);
}
/*
* Otherwise, you need to use this, which will obtain the mult/shift
* from the clock_data structure. Use init_sched_clock() with this.
*/
static inline unsigned long long cyc_to_sched_clock(struct clock_data *cd,
u32 cyc, u32 mask)
{
return cyc_to_fixed_sched_clock(cd, cyc, mask, cd->mult, cd->shift);
}
/*
* Initialize the clock data - calculate the appropriate multiplier
* and shift. Also setup a timer to ensure that the epoch is refreshed
* at the appropriate time interval, which will call your update
* handler.
*/
void init_sched_clock(struct clock_data *, void (*)(void),
unsigned int, unsigned long);
/*
* Use this initialization function rather than init_sched_clock() if
* you're using cyc_to_fixed_sched_clock, which will warn if your
* constants are incorrect.
*/
static inline void init_fixed_sched_clock(struct clock_data *cd,
void (*update)(void), unsigned int bits, unsigned long rate,
u32 mult, u32 shift)
{
init_sched_clock(cd, update, bits, rate);
if (cd->mult != mult || cd->shift != shift) {
pr_crit("sched_clock: wrong multiply/shift: %u>>%u vs calculated %u>>%u\n"
"sched_clock: fix multiply/shift to avoid scheduler hiccups\n",
mult, shift, cd->mult, cd->shift);
}
}
#endif
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