On 08/20/2010 02:02 PM, john stultz wrote:
On Fri, 2010-08-20 at 13:37 -1000, Zachary Amsden wrote:
On 08/20/2010 08:39 AM, john stultz wrote:
On Thu, 2010-08-19 at 22:07 -1000, Zachary Amsden wrote:
Add a kernel call to get the number of nanoseconds since boot. This
is generally useful enough to make it a generic call.
Few comments here.
Signed-off-by: Zachary Amsden<zamsden@xxxxxxxxxx>
---
include/linux/time.h | 1 +
kernel/time/timekeeping.c | 27 +++++++++++++++++++++++++++
2 files changed, 28 insertions(+), 0 deletions(-)
diff --git a/include/linux/time.h b/include/linux/time.h
index ea3559f..5d04108 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -145,6 +145,7 @@ extern void getnstimeofday(struct timespec *tv);
extern void getrawmonotonic(struct timespec *ts);
extern void getboottime(struct timespec *ts);
extern void monotonic_to_bootbased(struct timespec *ts);
+extern s64 getnsboottime(void);
So instead of converting the timespec from getboottime, why did you add
a new interface? Also if not a timespec, why did you pick a s64 instead
of a ktime_t?
The new interface was suggested several times, so I'm proposing it. I'm
indifferent to putting it the kernel API or making it internal to KVM.
KVM doesn't want to deal with conversions to / from ktime_t; this code
uses a lot (too much) math, and it's easy to get wrong when splitting
sec / nsec fields. So s64 seems a natural type for ns values. I
realize it's not entirely consistent with the kernel API, but s64
representation for ns seems to be creeping in.
I can understand wanting that, way back I was pushing for s64 ns
representations for most time values, but the ktime_t was considered a
reasonable compromise to avoid costly 64bit divides to split (sec,nsec)
on 32bit arches.
We want time in simply parseable formats, so we always end up with sec /
msec, sec / usec, sec / nsec. This is simply a convenient
representation for humans. Programmers always end up copying this model
and it causes so many lovely bugs. How many times can you race while
reading CMOS Y/M/D/H/S?
Fortunately now that 64-bit computing is nearly pervasive, we can make
most of these problems go away.
I think gettimefromboot_ns() is a good descriptive name, but slightly
too long - it would ruin my indentation. Perhaps getrealtime_ns()?
Zach
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