Date: Thu, 27 Oct 2011 13:39:51 -0700 From: Matthew Jacob <mj@feral.com> To: freebsd-arch@freebsd.org Subject: Re: newbus IO ordering semantics - moving forward Message-ID: <4EA9C197.9080407@feral.com> In-Reply-To: <CAJ-VmonFJG3xLn2JvarOUN6o-e7MC%2BA%2B=W9_vocZqY6L3CmTmQ@mail.gmail.com> References: <CAJ-VmonFJG3xLn2JvarOUN6o-e7MC%2BA%2B=W9_vocZqY6L3CmTmQ@mail.gmail.com>
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On 10/27/2011 1:28 PM, Adrian Chadd wrote:
> * Make the bus default to use ordered semantics, much like what Linux
> does - ie, all IO read/writes (io or memory) are in-order and flushed
> with a barrier;
> * Add an option which allows the driver to request a region with
> loose-running/lazy semantics, what we're supposed to have now, and
> then leave barriers up to the driver;
> * Print out something nice and loud if a driver decides to use the
> lazy/loose semantics, which may result in unpredictable behaviour on
> non-{i386,amd64}.
>
> I'd appreciate some feedback/comments before I go off and code all of this up.
>
>
No. Please don't change the current semantics which are well understood
if only fitfully adhered to. This would put us in the position of having
some drivers possibly work slower because they didn't do the "lazy" request.
I also am not sure I agree with your characterization of linux semantics.
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