Messages in this thread | | | Date | Thu, 13 Jul 2017 16:42:05 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support |
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On Thu, Jul 13, 2017 at 03:04:09PM +0100, Sudeep Holla wrote:
> The question is whether we *need* to know the completion of frequency > transition. What is the impact of absence of it ? I am considering > platforms which may take up to a ms or more to do the actual transition > in the firmware.
So on x86 we can recover from not knowing by means of the APERF/MPERF thing, which gives us the average effective frequency over the last period.
If you lack that you need something to update the actual effective frequency.
Changing the effective frequency at request time might confuse things -- esp. if the request might not be honoured at all or can take a significant time to complete. Not to mention that _IF_ you rely on the effective frequency to set other clocks things can come unstuck.
So unless you go the whole distance and do APERF/MPERF like things, I think it would be very good to have a notification of completion (and possibly a read-back of the effective frequency that is now set).
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