linux-kernel - Re: [PATCH 04/14] init: deps: order network interfaces by link order

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Date:	Mon, 19 Oct 2015 12:57:51 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH 04/14] init: deps: order network interfaces by link order

Am 18.10.2015 um 12:11 schrieb Alexander Holler:
> Am 18.10.2015 um 07:59 schrieb Greg Kroah-Hartman:
>> On Sun, Oct 18, 2015 at 07:20:34AM +0200, Alexander Holler wrote:
>>> Am 18.10.2015 um 07:14 schrieb Greg Kroah-Hartman:
>>>> On Sun, Oct 18, 2015 at 06:59:22AM +0200, Alexander Holler wrote:
>>>>> Am 17.10.2015 um 21:36 schrieb Greg Kroah-Hartman:
>>>>>
>>>>>> Again, parallelizing does not solve anything, and causes more
>>>>>> problems
>>>>>> _and_ makes things take longer.  Try it, we have done it in the
>>>>>> past and
>>>>>> proven this, it's pretty easy to test :)
>>>>>
>>>>> Just because I'm curious, may I ask how I would test that in the
>>>>> easy way
>>>>> you have in mind? I've just posted the results of my tests (the patch
>>>>> series) but I wonder what you do have in mind.
>>>>
>>>> Use the tool, scripts/bootgraph.pl to create a boot graph of your boot
>>>> sequence.  That should show you the drivers, or other areas, that are
>>>> causing your boot to be "slow".
>>>
>>> So I've misunderstood you. I've read your paragraph as that it's easy to
>>> test parallelizing.
>>
>> Ah, ok, if you want to parallelize everything, add some logic in the
>> driver core where the probe() callback is made to spin that off into a
>> new thread for every call, and when it's done, clean up the thread.
>> That's what I did many years ago to try this all out, if you dig in the
>> lkml archives there's probably a patch somewhere that you can base the
>> work off of to test it yourself.
>
> Hmm, I don't think I will do that because that means to setup a new
> thread for every call. And it doesn't need much imagination (or
> experience) that this introduces quite some overhead.
>
> But maybe it makes sense to try out what I'm doing in my patches,
> starting multiple threads once and then just giving them some work. Will

After a having second thought on your simple approach to parallelize 
stuff, I have to say that it just can't work because just starting a 
thread for every probe() totally ignores possible dependencies. 
Regardless if using one thread per probe() call or if feeding probe() 
calls to just a few threads.

Maybe that's why previous attempts to parallelize stuff failed. But 
that's just an assumption as I'm unaware of these previous attempts.

Regards,

Alexander Holler
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