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timers, sched/clock: Remove suspend from clock_read_data() 

Currently cd.read_data.suspended is read by the hotpath function
sched_clock(). This variable need not be accessed on the
hotpath. In fact, once it is removed, we can remove the
conditional branches from sched_clock() and install a dummy
read_sched_clock function to suspend the clock.

The new master copy of the function pointer
(actual_read_sched_clock) is introduced and is used for all
reads of the clock hardware except those within sched_clock
itself.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1427397806-20889-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Daniel Thompson 2015-03-26 12:23:24 -07:00 committed by Ingo Molnar
parent cf7c9c1707
commit 13dbeb384d
1 changed files with 25 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
kernel/time/sched_clock.c
View File

@ -28,10 +28,9 @@
* @read_sched_clock: Current clock source (or dummy source when suspended)
* @mult: Multipler for scaled math conversion
* @shift: Shift value for scaled math conversion
* @suspended: Flag to indicate if the clock is suspended (stopped)
*
* Care must be taken when updating this structure; it is read by
* some very hot code paths. It occupies <=48 bytes and, when combined
* some very hot code paths. It occupies <=40 bytes and, when combined
* with the seqcount used to synchronize access, comfortably fits into
* a 64 byte cache line.
*/
@ -42,7 +41,6 @@ struct clock_read_data {
u64 (*read_sched_clock)(void);
u32 mult;
u32 shift;
bool suspended;
};
/**
@ -64,6 +62,7 @@ struct clock_data {
struct clock_read_data read_data;
ktime_t wrap_kt;
unsigned long rate;
u64 (*actual_read_sched_clock)(void);
};
static struct hrtimer sched_clock_timer;
@ -83,6 +82,8 @@ static u64 notrace jiffy_sched_clock_read(void)
static struct clock_data cd ____cacheline_aligned = {
.read_data = { .mult = NSEC_PER_SEC / HZ,
.read_sched_clock = jiffy_sched_clock_read, },
.actual_read_sched_clock = jiffy_sched_clock_read,
};
static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
@ -99,12 +100,9 @@ unsigned long long notrace sched_clock(void)
do {
seq = raw_read_seqcount_begin(&cd.seq);
res = rd->epoch_ns;
if (!rd->suspended) {
cyc = rd->read_sched_clock();
cyc = (cyc - rd->epoch_cyc) & rd->sched_clock_mask;
res += cyc_to_ns(cyc, rd->mult, rd->shift);
}
cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
rd->sched_clock_mask;
res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
} while (read_seqcount_retry(&cd.seq, seq));
return res;
@ -120,7 +118,7 @@ static void notrace update_sched_clock(void)
u64 ns;
struct clock_read_data *rd = &cd.read_data;
cyc = rd->read_sched_clock();
cyc = cd.actual_read_sched_clock();
ns = rd->epoch_ns +
cyc_to_ns((cyc - rd->epoch_cyc) & rd->sched_clock_mask,
rd->mult, rd->shift);
@ -166,10 +164,11 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
/* update epoch for new counter and update epoch_ns from old counter*/
new_epoch = read();
cyc = rd->read_sched_clock();
cyc = cd.actual_read_sched_clock();
ns = rd->epoch_ns +
cyc_to_ns((cyc - rd->epoch_cyc) & rd->sched_clock_mask,
rd->mult, rd->shift);
cd.actual_read_sched_clock = read;
raw_write_seqcount_begin(&cd.seq);
rd->read_sched_clock = read;
@ -209,7 +208,7 @@ void __init sched_clock_postinit(void)
* If no sched_clock function has been provided at that point,
* make it the final one one.
*/
if (cd.read_data.read_sched_clock == jiffy_sched_clock_read)
if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
update_sched_clock();
@ -223,13 +222,24 @@ void __init sched_clock_postinit(void)
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
}
/*
* Clock read function for use when the clock is suspended.
*
* This function makes it appear to sched_clock() as if the clock
* stopped counting at its last update.
*/
static u64 notrace suspended_sched_clock_read(void)
{
return cd.read_data.epoch_cyc;
}
static int sched_clock_suspend(void)
{
struct clock_read_data *rd = &cd.read_data;
update_sched_clock();
hrtimer_cancel(&sched_clock_timer);
rd->suspended = true;
rd->read_sched_clock = suspended_sched_clock_read;
return 0;
}
@ -237,9 +247,9 @@ static void sched_clock_resume(void)
{
struct clock_read_data *rd = &cd.read_data;
rd->epoch_cyc = rd->read_sched_clock();
rd->epoch_cyc = cd.actual_read_sched_clock();
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
rd->suspended = false;
rd->read_sched_clock = cd.actual_read_sched_clock;
}
static struct syscore_ops sched_clock_ops = {