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timers, sched/clock: Clean up the code a bit 

Trivial cleanups, to improve the readability of the generic sched_clock() code:

 - Improve and standardize comments
 - Standardize the coding style
 - Use vertical spacing where appropriate
 - etc.

No code changed:

  md5:
    19a053b31e0c54feaeff1492012b019a  sched_clock.o.before.asm
    19a053b31e0c54feaeff1492012b019a  sched_clock.o.after.asm

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar 2015-03-27 07:08:06 +01:00
parent 1809bfa44e
commit 32fea568ae
1 changed files with 55 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

105
kernel/time/sched_clock.c
View File

@ -1,5 +1,6 @@
/* /*
* sched_clock.c: support for extending counters to full 64-bit ns counter * sched_clock.c: Generic sched_clock() support, to extend low level
* hardware time counters to full 64-bit ns values.
* *
* This program is free software; you can redistribute it and/or modify * 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 * it under the terms of the GNU General Public License version 2 as
@ -19,15 +20,15 @@
#include <linux/bitops.h> #include <linux/bitops.h>
/** /**
* struct clock_read_data - data required to read from sched_clock * struct clock_read_data - data required to read from sched_clock()
* *
* @epoch_ns: sched_clock value at last update * @epoch_ns: sched_clock() value at last update
* @epoch_cyc: Clock cycle value at last update * @epoch_cyc: Clock cycle value at last update.
* @sched_clock_mask: Bitmask for two's complement subtraction of non 64bit * @sched_clock_mask: Bitmask for two's complement subtraction of non 64bit
* clocks * clocks.
* @read_sched_clock: Current clock source (or dummy source when suspended) * @read_sched_clock: Current clock source (or dummy source when suspended).
* @mult: Multipler for scaled math conversion * @mult: Multipler for scaled math conversion.
* @shift: Shift value for scaled math conversion * @shift: Shift value for scaled math conversion.
* *
* Care must be taken when updating this structure; it is read by * Care must be taken when updating this structure; it is read by
* some very hot code paths. It occupies <=40 bytes and, when combined * some very hot code paths. It occupies <=40 bytes and, when combined
@ -44,25 +45,26 @@ struct clock_read_data {
}; };
/** /**
* struct clock_data - all data needed for sched_clock (including * struct clock_data - all data needed for sched_clock() (including
* registration of a new clock source) * registration of a new clock source)
* *
* @seq: Sequence counter for protecting updates. The lowest * @seq: Sequence counter for protecting updates. The lowest
* bit is the index for @read_data. * bit is the index for @read_data.
* @read_data: Data required to read from sched_clock. * @read_data: Data required to read from sched_clock.
* @wrap_kt: Duration for which clock can run before wrapping * @wrap_kt: Duration for which clock can run before wrapping.
* @rate: Tick rate of the registered clock * @rate: Tick rate of the registered clock.
* @actual_read_sched_clock: Registered clock read function * @actual_read_sched_clock: Registered hardware level clock read function.
* *
* The ordering of this structure has been chosen to optimize cache * The ordering of this structure has been chosen to optimize cache
* performance. In particular seq and read_data[0] (combined) should fit * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
* into a single 64 byte cache line. * into a single 64-byte cache line.
*/ */
struct clock_data { struct clock_data {
seqcount_t seq; seqcount_t seq;
struct clock_read_data read_data[2]; struct clock_read_data read_data[2];
ktime_t wrap_kt; ktime_t wrap_kt;
unsigned long rate; unsigned long rate;
u64 (*actual_read_sched_clock)(void); u64 (*actual_read_sched_clock)(void);
}; };
@ -112,10 +114,10 @@ unsigned long long notrace sched_clock(void)
/* /*
* Updating the data required to read the clock. * Updating the data required to read the clock.
* *
* sched_clock will never observe mis-matched data even if called from * sched_clock() will never observe mis-matched data even if called from
* an NMI. We do this by maintaining an odd/even copy of the data and * an NMI. We do this by maintaining an odd/even copy of the data and
* steering sched_clock to one or the other using a sequence counter. * steering sched_clock() to one or the other using a sequence counter.
* In order to preserve the data cache profile of sched_clock as much * In order to preserve the data cache profile of sched_clock() as much
* as possible the system reverts back to the even copy when the update * as possible the system reverts back to the even copy when the update
* completes; the odd copy is used *only* during an update. * completes; the odd copy is used *only* during an update.
*/ */
@ -135,7 +137,7 @@ static void update_clock_read_data(struct clock_read_data *rd)
} }
/* /*
* Atomically update the sched_clock epoch. * Atomically update the sched_clock() epoch.
*/ */
static void update_sched_clock(void) static void update_sched_clock(void)
{ {
@ -146,9 +148,7 @@ static void update_sched_clock(void)
rd = cd.read_data[0]; rd = cd.read_data[0];
cyc = cd.actual_read_sched_clock(); cyc = cd.actual_read_sched_clock();
ns = rd.epoch_ns + ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask,
rd.mult, rd.shift);
rd.epoch_ns = ns; rd.epoch_ns = ns;
rd.epoch_cyc = cyc; rd.epoch_cyc = cyc;
@ -160,11 +160,12 @@ static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
{ {
update_sched_clock(); update_sched_clock();
hrtimer_forward_now(hrt, cd.wrap_kt); hrtimer_forward_now(hrt, cd.wrap_kt);
return HRTIMER_RESTART; return HRTIMER_RESTART;
} }
void __init sched_clock_register(u64 (*read)(void), int bits, void __init
unsigned long rate) sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
{ {
u64 res, wrap, new_mask, new_epoch, cyc, ns; u64 res, wrap, new_mask, new_epoch, cyc, ns;
u32 new_mult, new_shift; u32 new_mult, new_shift;
@ -177,51 +178,53 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
WARN_ON(!irqs_disabled()); WARN_ON(!irqs_disabled());
/* calculate the mult/shift to convert counter ticks to ns. */ /* Calculate the mult/shift to convert counter ticks to ns. */
clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600); clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
new_mask = CLOCKSOURCE_MASK(bits); new_mask = CLOCKSOURCE_MASK(bits);
cd.rate = rate; cd.rate = rate;
/* calculate how many nanosecs until we risk wrapping */ /* Calculate how many nanosecs until we risk wrapping */
wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL); wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
cd.wrap_kt = ns_to_ktime(wrap); cd.wrap_kt = ns_to_ktime(wrap);
rd = cd.read_data[0]; rd = cd.read_data[0];
/* update epoch for new counter and update epoch_ns from old counter*/ /* Update epoch for new counter and update 'epoch_ns' from old counter*/
new_epoch = read(); new_epoch = read();
cyc = cd.actual_read_sched_clock(); cyc = cd.actual_read_sched_clock();
ns = rd.epoch_ns + ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask,
rd.mult, rd.shift);
cd.actual_read_sched_clock = read; cd.actual_read_sched_clock = read;
rd.read_sched_clock = read; rd.read_sched_clock = read;
rd.sched_clock_mask = new_mask; rd.sched_clock_mask = new_mask;
rd.mult = new_mult; rd.mult = new_mult;
rd.shift = new_shift; rd.shift = new_shift;
rd.epoch_cyc = new_epoch; rd.epoch_cyc = new_epoch;
rd.epoch_ns = ns; rd.epoch_ns = ns;
update_clock_read_data(&rd); update_clock_read_data(&rd);
r = rate; r = rate;
if (r >= 4000000) { if (r >= 4000000) {
r /= 1000000; r /= 1000000;
r_unit = 'M'; r_unit = 'M';
} else if (r >= 1000) { } else {
r /= 1000; if (r >= 1000) {
r_unit = 'k'; r /= 1000;
} else r_unit = 'k';
r_unit = ' '; } else {
r_unit = ' ';
}
}
/* calculate the ns resolution of this counter */ /* Calculate the ns resolution of this counter */
res = cyc_to_ns(1ULL, new_mult, new_shift); res = cyc_to_ns(1ULL, new_mult, new_shift);
pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n", pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
bits, r, r_unit, res, wrap); bits, r, r_unit, res, wrap);
/* Enable IRQ time accounting if we have a fast enough sched_clock */ /* Enable IRQ time accounting if we have a fast enough sched_clock() */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000)) if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime(); enable_sched_clock_irqtime();
@ -231,7 +234,7 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
void __init sched_clock_postinit(void) void __init sched_clock_postinit(void)
{ {
/* /*
* If no sched_clock function has been provided at that point, * If no sched_clock() function has been provided at that point,
* make it the final one one. * make it the final one one.
*/ */
if (cd.actual_read_sched_clock == jiffy_sched_clock_read) if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
@ -257,7 +260,7 @@ void __init sched_clock_postinit(void)
* This function must only be called from the critical * This function must only be called from the critical
* section in sched_clock(). It relies on the read_seqcount_retry() * section in sched_clock(). It relies on the read_seqcount_retry()
* at the end of the critical section to be sure we observe the * at the end of the critical section to be sure we observe the
* correct copy of epoch_cyc. * correct copy of 'epoch_cyc'.
*/ */
static u64 notrace suspended_sched_clock_read(void) static u64 notrace suspended_sched_clock_read(void)
{ {
@ -273,6 +276,7 @@ static int sched_clock_suspend(void)
update_sched_clock(); update_sched_clock();
hrtimer_cancel(&sched_clock_timer); hrtimer_cancel(&sched_clock_timer);
rd->read_sched_clock = suspended_sched_clock_read; rd->read_sched_clock = suspended_sched_clock_read;
return 0; return 0;
} }
@ -286,13 +290,14 @@ static void sched_clock_resume(void)
} }
static struct syscore_ops sched_clock_ops = { static struct syscore_ops sched_clock_ops = {
.suspend = sched_clock_suspend, .suspend = sched_clock_suspend,
.resume = sched_clock_resume, .resume = sched_clock_resume,
}; };
static int __init sched_clock_syscore_init(void) static int __init sched_clock_syscore_init(void)
{ {
register_syscore_ops(&sched_clock_ops); register_syscore_ops(&sched_clock_ops);
return 0; return 0;
} }
device_initcall(sched_clock_syscore_init); device_initcall(sched_clock_syscore_init);