linux-kernel - Re: [PATCH] driver-core: remove lock for platform devices during probe

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Date:   Mon, 24 Apr 2017 09:46:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     weili@...eaurora.org
Cc:     linux-kernel@...r.kernel.org, vatsa@...eaurora.org
Subject: Re: [PATCH] driver-core: remove lock for platform devices during
 probe

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

On Mon, Apr 24, 2017 at 04:27:44PM +0800, weili@...eaurora.org wrote:
> Hi Greg,
> 
>    We are optimizing boot time for Linux kernel and try to make some
> platform drivers use asynchronous probe(by changing probe type of driver to
> PROBE_PREFER_ASYNCHRONOUS) to reduce boot time. However we found the
> platform drivers did not probe in parallel because they will lock the same
> parent device(platform bus for platform drivers) during probe.  So we add
> this patch to remove lock of parent for platform device. This will help to
> make platform driver probe in parallel and reduce boot time.

And does it really reduce boot time?  What are the numbers?  Why do you
have so many platform devices and not "real bus" devices?  What does the
boot graph look like when you run with and without this patch?  Why is
the platform bus so "special" to warrant this?  Should we perhaps make
this an option for any bus to enable/disable?

In other words, you need to provide a whole lot more information here,
justify why you are doing this type of change, and fix the issue I
pointed out, in order to get such a chance accepted.

Come on now, you know better than this...

greg k-h