linux-kernel - Re: [PATCH] of: reduce the number of PROBE

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Date:	Thu, 22 Aug 2013 11:20:19 +0100
From:	Grant Likely <grant.likely@...aro.org>
To:	Jean-Francois Moine <moinejf@...e.fr>
Cc:	Rob Herring <rob.herring@...xeda.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] of: reduce the number of PROBE_DEFERs

On Thu, Aug 22, 2013 at 9:00 AM, Jean-Francois Moine <moinejf@...e.fr> wrote:
> On Tue, 20 Aug 2013 11:13:24 +0100
> Grant Likely <grant.likely@...aro.org> wrote:
>
>> On Tue, Aug 20, 2013 at 11:01 AM, Jean-Francois Moine <moinejf@...e.fr> wrote:
>> > This patch populates the platform from the device tree into two steps:
>> > the first step creates the nodes that are referenced by a phandle,
>> > the second step creates the other nodes.
>> >
>> > This permits to reduce the number of PROBE_DEFERs.
>> >
>> > Signed-off-by: Jean-Francois Moine <moinejf@...e.fr>
>> > ---
>> > A better way to reduce probe deferral could be sorting the nodes
>> > according to their phandle level in the DT blob at compilation time ...
>>
>> Have you got measurements or statistics that show this making a
>> difference? I suspect you'll find for boot time it will have little to
>> no affect since the device driver probe order is more closely related
>> to the kernel link order than the order that devices were registered.
>
> With the device tree and most drivers as modules, the kernel link order
> does not matter.
>
> I admit that the gain may be small: I just get none or just one probe
> deferral instead of 3 on my cubox with this patch.

If you've only got 3 probe deferrals, then is this really an issue
worth complicating the code over? I'd like to see a more significant
impact before taking this step.

g.
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