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SubjectRe: [RFC v7 00/23] adapt clockevents frequencies to mono clock
Date
Thomas Gleixner <tglx@linutronix.de> writes:

> On Fri, 16 Sep 2016, Nicolai Stange wrote:
>
>> Goal: avoid programming ced devices too early for large deltas, for
>> details, c.f. the description of [21/23].
>>
>> [21-23/23] Actually do the frequency adjustments.
>>
>> Tested on x86_64 and next-20160916.
>
> Have you ever measured the overhead of the extra work which has to be done
> in clockevents_adjust_all_freqs() ?

Not exactly, I had a look at its invocation frequency which seems to
decay exponentially with uptime, presumably because the NTP error
approaches zero.

However, I've just gathered a function_graph ftrace on my Intel
i7-4800MQ (Haswell, 8HTs):

# tracer: function_graph
#
# TIME CPU DURATION FUNCTION CALLS
# | | | | | | | |
85.287027 | 0) 0.899 us | clockevents_adjust_all_freqs();
85.288026 | 0) 0.759 us | clockevents_adjust_all_freqs();
85.289026 | 0) 0.735 us | clockevents_adjust_all_freqs();
85.290026 | 0) 0.671 us | clockevents_adjust_all_freqs();
149.503656 | 2) 2.477 us | clockevents_adjust_all_freqs();
149.507660 | 2) 2.308 us | clockevents_adjust_all_freqs();
149.511658 | 2) 2.651 us | clockevents_adjust_all_freqs();
149.545660 | 0) 2.268 us | clockevents_adjust_all_freqs();
149.564211 | 2) 2.321 us | clockevents_adjust_all_freqs();
214.351899 | 2) 1.520 us | clockevents_adjust_all_freqs();
214.354935 | 0) 1.053 us | clockevents_adjust_all_freqs();
279.026205 | 0) 2.289 us | clockevents_adjust_all_freqs();
279.030195 | 0) 2.190 us | clockevents_adjust_all_freqs();
279.034196 | 0) 2.381 us | clockevents_adjust_all_freqs();
279.047492 | 2) 2.390 us | clockevents_adjust_all_freqs();
344.250356 | 1) 2.727 us | clockevents_adjust_all_freqs();
408.879538 | 1) 2.235 us | clockevents_adjust_all_freqs();
473.125730 | 6) 1.513 us | clockevents_adjust_all_freqs();
473.129731 | 6) 1.650 us | clockevents_adjust_all_freqs();
538.387891 | 3) 2.305 us | clockevents_adjust_all_freqs();
538.391890 | 3) 2.300 us | clockevents_adjust_all_freqs();
668.257162 | 3) 2.691 us | clockevents_adjust_all_freqs();
668.261162 | 3) 2.306 us | clockevents_adjust_all_freqs();
733.459261 | 0) 1.066 us | clockevents_adjust_all_freqs();
733.463261 | 0) 1.233 us | clockevents_adjust_all_freqs();
733.467263 | 1) 1.382 us | clockevents_adjust_all_freqs();
863.398561 | 2) 2.218 us | clockevents_adjust_all_freqs();
863.402552 | 2) 2.792 us | clockevents_adjust_all_freqs();
1122.210001 | 3) 2.259 us | clockevents_adjust_all_freqs();
1122.214004 | 3) 2.165 us | clockevents_adjust_all_freqs();
1381.283287 | 2) 1.944 us | clockevents_adjust_all_freqs();
1895.664008 | 2) 1.940 us | clockevents_adjust_all_freqs();
1895.668009 | 2) 2.041 us | clockevents_adjust_all_freqs();
2930.385388 | 0) 1.067 us | clockevents_adjust_all_freqs();
2930.386390 | 5) 1.208 us | clockevents_adjust_all_freqs();


Thanks,

Nicolai

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