RE: [PATCH v3 1/4] Add correlated clocksource deriving system time from an auxiliary clocksource

From: Thomas Gleixner
Date: Fri Sep 04 2015 - 09:03:26 EST

On Thu, 3 Sep 2015, Hall, Christopher S wrote:

Can you please teach your mail client to add proper line breaks around
80? Your mail renders horrible in a text based mail client.

> In addition to the network interface, ART will be used in the audio
> interface as well. We need to support the case where an audio
> co-processor will control the audio device. In this case, the
> get_ts() function supplied by the audio driver will be very slow
> (several milliseconds) and the result will be out of date by some
> fraction of that amount.

You are not telling at all, what this driver is supposed to do, what
this get_ts() function is for and how that co-processor thing works.

You just make claims, that you need this without explaining WHY. And
that WHY is the most interesting part.

> This loop makes strict requirements on the latency and recency. Is
> it possible to relax that requirement in some way?

No. This function is explicitely for the precise timestamp usecase,
which is required by PTP and other sane use cases.

> For example, supply the ART value as an argument and, in the case of
> the realtime clock, keep a short history of clock changes. It would

It's not only clock realtime which is affected by those.

> fail in cases where there are a lot of calls to adjtimex(),

That has nothing to do with lots of adjtimex calls. The kernel does a
slow correction of the conversion values itself to avoid time jumping

> but it will would work most of the time.

Will, would, most? - Could, perhaps, sometimes?

Looks like a design from the trainwreck engineering departement. We
want to have it very precise, but we don't care if it behaves like a
random number generator.

Can you folks please get your act together and provide coherent
explanations about the usecase and the constraints instead of
proposing random functions with obscure semantics?


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