[patch 43/55] x86: kvm: Make kvm_get_time_and_clockread() nanoseconds based

From: Thomas Gleixner
Date: Fri Jul 11 2014 - 09:45:37 EST


Convert the relevant base data right away to nanoseconds instead of
doing the conversion on every readout. Reduces text size by 160 bytes.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
---
arch/x86/kvm/x86.c | 44 ++++++++++++++------------------------------
1 file changed, 14 insertions(+), 30 deletions(-)

Index: tip/arch/x86/kvm/x86.c
===================================================================
--- tip.orig/arch/x86/kvm/x86.c
+++ tip/arch/x86/kvm/x86.c
@@ -984,9 +984,8 @@ struct pvclock_gtod_data {
u32 shift;
} clock;

- /* open coded 'struct timespec' */
- u64 monotonic_time_snsec;
- time_t monotonic_time_sec;
+ u64 boot_ns;
+ u64 nsec_base;
};

static struct pvclock_gtod_data pvclock_gtod_data;
@@ -994,6 +993,9 @@ static struct pvclock_gtod_data pvclock_
static void update_pvclock_gtod(struct timekeeper *tk)
{
struct pvclock_gtod_data *vdata = &pvclock_gtod_data;
+ u64 boot_ns;
+
+ boot_ns = ktime_to_ns(ktime_add(tk->base_mono, tk->offs_boot));

write_seqcount_begin(&vdata->seq);

@@ -1004,17 +1006,8 @@ static void update_pvclock_gtod(struct t
vdata->clock.mult = tk->mult;
vdata->clock.shift = tk->shift;

- vdata->monotonic_time_sec = tk->xtime_sec
- + tk->wall_to_monotonic.tv_sec;
- vdata->monotonic_time_snsec = tk->xtime_nsec
- + (tk->wall_to_monotonic.tv_nsec
- << tk->shift);
- while (vdata->monotonic_time_snsec >=
- (((u64)NSEC_PER_SEC) << tk->shift)) {
- vdata->monotonic_time_snsec -=
- ((u64)NSEC_PER_SEC) << tk->shift;
- vdata->monotonic_time_sec++;
- }
+ vdata->boot_ns = boot_ns;
+ vdata->nsec_base = tk->xtime_nsec;

write_seqcount_end(&vdata->seq);
}
@@ -1371,23 +1364,22 @@ static inline u64 vgettsc(cycle_t *cycle
return v * gtod->clock.mult;
}

-static int do_monotonic(struct timespec *ts, cycle_t *cycle_now)
+static int do_monotonic_boot(s64 *t, cycle_t *cycle_now)
{
+ struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
unsigned long seq;
- u64 ns;
int mode;
- struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
+ u64 ns;

- ts->tv_nsec = 0;
do {
seq = read_seqcount_begin(&gtod->seq);
mode = gtod->clock.vclock_mode;
- ts->tv_sec = gtod->monotonic_time_sec;
- ns = gtod->monotonic_time_snsec;
+ ns = gtod->nsec_base;
ns += vgettsc(cycle_now);
ns >>= gtod->clock.shift;
+ ns += gtod->boot_ns;
} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
- timespec_add_ns(ts, ns);
+ *t = ns;

return mode;
}
@@ -1395,19 +1387,11 @@ static int do_monotonic(struct timespec
/* returns true if host is using tsc clocksource */
static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
{
- struct timespec ts;
-
/* checked again under seqlock below */
if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
return false;

- if (do_monotonic(&ts, cycle_now) != VCLOCK_TSC)
- return false;
-
- monotonic_to_bootbased(&ts);
- *kernel_ns = timespec_to_ns(&ts);
-
- return true;
+ return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
}
#endif



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/