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From: John Baldwin <jhb@freebsd.org>
To: Randall Stewart <rrs@lakerest.net>
Subject: Re: Driver patch to look at...
Date: Tue, 5 Feb 2013 14:11:17 -0500
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 (bigwig.baldwin.cx); Tue, 05 Feb 2013 14:11:19 -0500 (EST)
Cc: freebsd-net@freebsd.org, Robert Watson <rwatson@freebsd.org>,
 Jack Vogel <jfvogel@gmail.com>, Kip Macy <kmacy@freebsd.org>
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On Tuesday, February 05, 2013 2:04:12 pm Randall Stewart wrote:
> Hmm
>=20
> That would trade off a stack pointer + a compare
> vs always doing the move.

Right, the store is probably cheaper than the branch. :)  However, minimizi=
ng=20
the duplicated code in drivers and having this interface be as clear/readab=
le=20
as possible is my main goal.

> Thats fine until I have to add the _mc() version, then the put
> back would be an atomic, and most of the time the return from
> this is probably not changed=85
>=20
> I really would prefer not to since the compare and maybe store vs
> the always store.. though the same now, would be far more expensive
> in the _mc version.. if we do a _mc version of course ;-)

I would just not bother with an _mc version until we actually need it. :)

I think doing the sort of peek/advance type logic only works well with
single consumers anyway.

=2D-=20
John Baldwin