On Thu, Feb 12, 2015 at 11:28:14AM +0100, Peter Zijlstra wrote:
> > and you would have to check the clocksource is TSC.
>
> It implicitly does that; it has that sched_clock_stable() thing, but
> yeah I suppose someone could change the clocksource even though the tsc
> is stable.
>
> Not using TSC when its available is quite crazy though.. but sure.
Something like this on top then.. it might have a few header issues, the
whole asm/tsc.h vs clocksource.h thing looks like pain.
I haven't tried to compile it, maybe we can move cycle_t into types and
fwd declare struct clocksource or whatnot.
Of course, all this is quite horrible on the timekeeping side; it might
be tglx and/or jstutlz are having spasms just reading it :-)
---
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1967,17 +1967,19 @@ static void local_clock_user_time(struct
cyc2ns_read_end(data);
}
-extern void notrace __ktime_get_mono_fast(u64 *offset, u32 *mult, u16 *shift);
+extern bool notrace __ktime_get_mono_fast(cycle_t (*read)(struct clocksource
*cs),
+ u64 *offset, u32 *mult, u16 *shift);
static void ktime_fast_mono_user_time(struct perf_event_mmap_page *userpg, u64
now)
{
+ if (!__ktime_get_mono_fast(read_tsc, &userpg->time_zero,
+ &userpg->time_mult,
+ &userpg->time_shift))
+ return;
+
userpg->cap_user_time = 1;
userpg->cap_user_time_zero = 1;
- __ktime_get_mono_fast(&userpg->time_zero,
- &userpg->time_mult,
- &userpg->time_shift);
-
userpg->offset = userpg->time_zero - now;
}
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -334,7 +334,8 @@ u64 notrace ktime_get_mono_fast_ns(void)
}
EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
-void notrace __ktime_get_mono_fast(u64 *offset, u32 *mult, u16 *shift)
+bool notrace __ktime_get_mono_fast(cycle_t (*read)(struct clocksource *),
+ u64 *offset, u32 *mult, u16 *shift)
{
struct tk_read_base *tkr;
unsigned int seq;
@@ -345,6 +346,9 @@ void notrace __ktime_get_mono_fast(u64 *
seq = raw_read_seqcount(&tk_fast_mono.seq);
tkr = tk_fast_mono.base + (seq & 0x01);
+ if (tkr->read != read)
+ return false;
+
cycle_now = tkr->read(tkr->clock);
delta = clocksource_delta(cycle_now, tkr->cycle_last,
tkr->mask);
@@ -362,6 +366,8 @@ void notrace __ktime_get_mono_fast(u64 *
*offset = now - nsec;
} while (read_seqcount_retry(&tk_fast_mono.seq, seq));
+
+ return true;
}
#ifdef CONFIG_GENERIC_TIME_VSYSCALL_OLD
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 94605c0e9cee..68e4039a58ea 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -32,6 +32,8 @@ static inline cycles_t get_cycles(void)
return ret;
}
+extern void cycle_t read_tsc(struct clocksource *);
+
static __always_inline cycles_t vget_cycles(void)
{
/*
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 505449700e0c..c580998f0160 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -965,7 +965,7 @@ static struct clocksource clocksource_tsc;
* checking the result of read_tsc() - cycle_last for being negative.
* That works because CLOCKSOURCE_MASK(64) does not mask out any bit.
*/
-static cycle_t read_tsc(struct clocksource *cs)
+cycle_t read_tsc(struct clocksource *cs)
{
return (cycle_t)get_cycles();
}
--
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