Messages in this thread | | | Date | Sun, 20 Oct 2013 09:34:56 +0200 | From | Andreas Mohr <> | Subject | Re: [PATCH 3/5] timer: Change idle/iowait accounting semantics |
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Hi,
just wanted to report that this capricious open-coded (ok, lone-coded :) converter:
+static inline ktime_t us_to_ktime(u64 us) +{ + static const ktime_t ktime_zero = { .tv64 = 0 }; + + return ktime_add_us(ktime_zero, us); +}
triggered a virtual red flag in my processing.
We obviously seem to be compensating for a domain mismatch here:
+ iowait = get_cpu_iowait_time_us(cpu, NULL); + + if (ktime_compare(idle, us_to_ktime(iowait)) > 0) + idle = ktime_sub_us(idle, iowait); +
And sure enough: get_cpu_iowait_time_us() does a final to-us conversion only right before result is returned, and it's located right within the same build unit (tick-sched.c). (and then we go ahead and do a from-us round trip :-P)
So, in case we want to standardize on ktime_t domain for these parts of purely *in-kernel* time handling, how about adding a _unit-local_ helper for providing a ktime-only result and convert get_cpu_iowait_time_us() into a simple to-us *external user code* one-line wrapper for it? (and include updates to all other places which would benefit from this change)
And preferably launch such patch as a preparatory patch for this subsequent 3/5 patch, within the series?
Unless I missed some other restrictions which cause us to need to cling to that manual from-us conversion, for now or forever...
Andreas Mohr
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