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

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DB02749AC@AcuExch.aculab.com>
Date:   Tue, 31 Jan 2017 10:03:26 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Mintz, Yuval'" <Yuval.Mintz@...ium.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.

From: Mintz, Yuval
> Sent: 30 January 2017 17:56
> > 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.

	David