netdev - Re: [PATCH 21/29] ioat2,3: dynamically resize descriptor ring

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Date:	Tue, 15 Sep 2009 16:07:05 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 21/29] ioat2,3: dynamically resize descriptor ring

On Mon, Sep 14, 2009 at 8:00 AM, Sosnowski, Maciej
<maciej.sosnowski@...el.com> wrote:
> Making the max_alloc_order a module parameter gives impression
> that it can be modified by an user, including making it larger than default.
> The default is however its maximum value, which may be confusing.
> Why not to use parameter only as the upper limit?

It is the upper limit.

The user can limit the upper size of the descriptor ring by setting
this to a value less than 16.  By default it is the maximum ring size
that the driver/hardware* supports.  Specifying values greater than 16
are not supported by the so we need enforce a ceiling at 16.

--
Dan

* We could support ring sizes larger than 1 << 16 but we would need to
extra logic to ensure that the pending count never exceeded 1 << 16.
Simpler I think to just limit the maximum ring size.
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