linux-kernel - Re: [PATCH 0/4] Fastboot revisited: Asynchronous function calls

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Message-ID: <20090104103104.6fdda9f2@infradead.org>
Date:	Sun, 4 Jan 2009 10:31:04 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, fweisbec@...il.com,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-acpi@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 0/4] Fastboot revisited: Asynchronous function calls

On Sun, 4 Jan 2009 10:16:57 -0800 (PST)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Sun, 4 Jan 2009, Arjan van de Ven wrote:
> > 
> > To see this working, I uploaded a "before" and "after" kernel
> > bootchart for one of my testboxes at
> > 
> > http://www.fenrus.org/linux/before.svg
> > http://www.fenrus.org/linux/after.svg
> 
> Ok, so why does the serial port init take so long? That's a quarter
> of a second for you, which is ridiculous.

good question; I was about to start looking into that one (but wanted
to get the patches out first before I did more than 3 to not waste time
on some dead-end approach if it ends up being that)

> 
> I _think_ it's the irq auto-probing, but that's just a guess.

I kinda was hoping that in part it was a scaling thing with the number
of ports (4 in my .config) so that I could do the ports
asynchronous compared to eachother ;-)

> The irq auto-probing itself also has a few excessive delays, like
> waiting for 0.1 s just to wait for spurious interrupts to trigger.
> Doing the extra unnecessary probe makes that doubly expensive.
> 
> Does this patch make any difference to you? I'm not at all sure that
> it's the irq probing, but if it is, then this should make the serial
> probe go much faster.

it turned it into a 25 msec deal .. pretty good improvement in my book.
(now I still might want to try to do this async so that it becomes
25/4 ... but the pressure i

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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