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From: Ingo Molnar on 12 Jun 2010 03:20

* Divyesh Shah <dpshah(a)google.com> wrote:

> This will take care of the pre-emptive kernel issue and the unbounded
> TSC drift problem. We will lose resolution though in some cases.

> - blkg->stats.start_group_wait_time = sched_clock();
> + blkg->stats.start_group_wait_time = ktime_to_ns(ktime_get());

Ugh!

ktime_get() can have insanely high overhead. Peter has added local_clock(), if
then you should use that and apply checks to make sure the result isnt
negative.

Ingo
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