linux-kernel - Re: [PATCH] usb: Use a workqueue in usb_add

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Message-ID: <CAPnjgZ0a4i1eGRK_pjKuiaG=sXKGCHT8kO4segHxqN6L2wm8Qw@mail.gmail.com>
Date:	Thu, 26 Jan 2012 15:48:43 -0800
From:	Simon Glass <sjg@...omium.org>
To:	Greg KH <gregkh@...e.de>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Subject: Re: [PATCH] usb: Use a workqueue in usb_add_hcd() to reduce boot time

Hi Greg,

On Tue, Jan 24, 2012 at 9:22 AM, Greg KH <gregkh@...e.de> wrote:
> On Tue, Jan 24, 2012 at 05:57:11PM +0100, Sebastian Andrzej Siewior wrote:
>> * Alan Stern | 2012-01-21 11:11:09 [-0500]:
>>
>> >Doing time-consuming things later won't make any difference.  That is,
>> >suppose the boot sequence performs activities A and B, where A takes a
>> >long time.  Doing A later, so that the boot sequence performs B and
>> >then A, won't change the total time required.
>>
>> That is true. However if you show the gui _now_ and look for USB later
>> then it feels faster and this is usually enough.
>
> Which has been done before, with great success (i.e. we did it for
> Moblin boot times), so it shouldn't be that big of an issue.
>
> Which points out the question, exactly what is the issue here?  We have
> "multithreaded" pci driver startup for a long time now, did that stop
> working here?  If you use bootchart, does it show that the USB host
> driver is stoping the machine from proceeding to the next stage in the
> boot process?
>
> From my experience, I never saw the USB host controller get in the way
> at all, it was always somethine else happening that caused problems
> (i.e. video.)
>
> Simon, do you have boot charts anywhere showing this?

I did have initcall timing when I last looked at this. USB was holding
up progress. Sorry for the delay - I hope to get back to this next
week.

Regards,
Simon

>
> thanks,
>
> greg k-h
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