netdev - RE: [PATCH net-next v2 2/2] qede: Add driver support for PTP.

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Date:   Tue, 31 Jan 2017 14:31:41 +0000
From:   "Mintz, Yuval" <Yuval.Mintz@...ium.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Richard Cochran' <richardcochran@...il.com>,
        "Kalluru, Sudarsana" <Sudarsana.Kalluru@...ium.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next v2 2/2] qede: Add driver support for PTP.

> > > How many different implementations of 'ops->adjfreq' are there?
> > > If there is only one you don't need an indirect call.
> >
> > There's only one implementation. But qed publishes its functions to
> > qede [and other modules] by structs of operations and not by exporting
> > symbols directly, and I don't see a reason to change that paradigm
> > here.
> > [Although I might be mistaken about that last bit]
> 
> If any of the functions are on 'hot paths' the cost of the indirect call is likely
> to be measurable.
> On a lot of cpus it will be a pipeline stall.
> The double-indirect almost certainly generates a stall.

I feel like I'm missing something. Again.
I thought the reasonable rate of rate-adjustment is once a second,
which doesn't make it 'hot' in any way.
In which scenario would we frequently encounter this configuration?