Skip to content

Commit

Permalink
sched/clock, x86: Move some cyc2ns() code around
Browse files Browse the repository at this point in the history 
There are no __cycles_2_ns() users outside of arch/x86/kernel/tsc.c,
so move it there.

There are no cycles_2_ns() users.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-01lslnavfgo3kmbo4532zlcj@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
  • Loading branch information
Peter Zijlstra authored and Ingo Molnar committed Jan 13, 2014
1 parent 5dd12c2 commit 57c67da
Show file tree
Hide file tree
Showing 2 changed files with 61 additions and 110 deletions.
59 changes: 0 additions & 59 deletions arch/x86/include/asm/timer.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,66 +13,7 @@ extern int recalibrate_cpu_khz(void);

extern int no_timer_check;

/* Accelerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
* ns = cycles * (ns_per_sec / freq)
* ns = cycles * (10^9 / (cpu_khz * 10^3))
* ns = cycles * (10^6 / cpu_khz)
*
* Then we use scaling math (suggested by george@mvista.com) to get:
* ns = cycles * (10^6 * SC / cpu_khz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
* We can use khz divisor instead of mhz to keep a better precision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*
* In:
*
* ns = cycles * cyc2ns_scale / SC
*
* Although we may still have enough bits to store the value of ns,
* in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
* leading to an incorrect result.
*
* To avoid this, we can decompose 'cycles' into quotient and remainder
* of division by SC. Then,
*
* ns = (quot * SC + rem) * cyc2ns_scale / SC
* = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
*
* - sqazi@google.com
*/

DECLARE_PER_CPU(unsigned long, cyc2ns);
DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);

#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns = this_cpu_read(cyc2ns_offset);
ns += mul_u64_u32_shr(cyc, this_cpu_read(cyc2ns), CYC2NS_SCALE_FACTOR);
return ns;
}

static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns;
unsigned long flags;

local_irq_save(flags);
ns = __cycles_2_ns(cyc);
local_irq_restore(flags);

return ns;
}

#endif /* _ASM_X86_TIMER_H */
112 changes: 61 additions & 51 deletions arch/x86/kernel/tsc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,66 @@ static int __read_mostly tsc_unstable;
static int __read_mostly tsc_disabled = -1;

int tsc_clocksource_reliable;

/* Accelerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
* ns = cycles * (ns_per_sec / freq)
* ns = cycles * (10^9 / (cpu_khz * 10^3))
* ns = cycles * (10^6 / cpu_khz)
*
* Then we use scaling math (suggested by george@mvista.com) to get:
* ns = cycles * (10^6 * SC / cpu_khz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
* We can use khz divisor instead of mhz to keep a better precision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*/

DEFINE_PER_CPU(unsigned long, cyc2ns);
DEFINE_PER_CPU(unsigned long long, cyc2ns_offset);

#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns = this_cpu_read(cyc2ns_offset);
ns += mul_u64_u32_shr(cyc, this_cpu_read(cyc2ns), CYC2NS_SCALE_FACTOR);
return ns;
}

static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
{
unsigned long long tsc_now, ns_now, *offset;
unsigned long flags, *scale;

local_irq_save(flags);
sched_clock_idle_sleep_event();

scale = &per_cpu(cyc2ns, cpu);
offset = &per_cpu(cyc2ns_offset, cpu);

rdtscll(tsc_now);
ns_now = cycles_2_ns(tsc_now);

if (cpu_khz) {
*scale = ((NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR) +
cpu_khz / 2) / cpu_khz;
*offset = ns_now - mult_frac(tsc_now, *scale,
(1UL << CYC2NS_SCALE_FACTOR));
}

sched_clock_idle_wakeup_event(0);
local_irq_restore(flags);
}

/*
* Scheduler clock - returns current time in nanosec units.
*/
Expand All @@ -62,7 +122,7 @@ u64 native_sched_clock(void)
rdtscll(this_offset);

/* return the value in ns */
return __cycles_2_ns(this_offset);
return cycles_2_ns(this_offset);
}

/* We need to define a real function for sched_clock, to override the
Expand Down Expand Up @@ -589,56 +649,6 @@ int recalibrate_cpu_khz(void)
EXPORT_SYMBOL(recalibrate_cpu_khz);


/* Accelerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
* ns = cycles * (ns_per_sec / freq)
* ns = cycles * (10^9 / (cpu_khz * 10^3))
* ns = cycles * (10^6 / cpu_khz)
*
* Then we use scaling math (suggested by george@mvista.com) to get:
* ns = cycles * (10^6 * SC / cpu_khz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
* We can use khz divisor instead of mhz to keep a better precision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*/

DEFINE_PER_CPU(unsigned long, cyc2ns);
DEFINE_PER_CPU(unsigned long long, cyc2ns_offset);

static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
{
unsigned long long tsc_now, ns_now, *offset;
unsigned long flags, *scale;

local_irq_save(flags);
sched_clock_idle_sleep_event();

scale = &per_cpu(cyc2ns, cpu);
offset = &per_cpu(cyc2ns_offset, cpu);

rdtscll(tsc_now);
ns_now = __cycles_2_ns(tsc_now);

if (cpu_khz) {
*scale = ((NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR) +
cpu_khz / 2) / cpu_khz;
*offset = ns_now - mult_frac(tsc_now, *scale,
(1UL << CYC2NS_SCALE_FACTOR));
}

sched_clock_idle_wakeup_event(0);
local_irq_restore(flags);
}

static unsigned long long cyc2ns_suspend;

void tsc_save_sched_clock_state(void)
Expand Down

0 comments on commit 57c67da

Please sign in to comment.