linux-kernel - RE: [BISECTED] EEE PC hangs when booting off battery

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Date:	Tue, 14 Apr 2009 08:55:58 -0700
From:	"Moore, Robert" <robert.moore@...el.com>
To:	Bjorn Helgaas <bjorn.helgaas@...com>,
	Arjan van de Ven <arjan@...radead.org>
CC:	Alan Jenkins <alan-jenkins@...fmail.co.uk>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Subject: RE: [BISECTED] EEE PC hangs when booting off battery

In fact, ACPI methods can execute concurrently -- constrained by the ACPI specification itself. The "big lock" is released before anything that will block for a significant amount of time, allowing other methods to run.

Bob


>-----Original Message-----
>From: linux-acpi-owner@...r.kernel.org [mailto:linux-acpi-
>owner@...r.kernel.org] On Behalf Of Bjorn Helgaas
>Sent: Tuesday, April 14, 2009 8:49 AM
>To: Arjan van de Ven
>Cc: Alan Jenkins; linux-acpi@...r.kernel.org; linux-kernel; Kernel Testers
>List; Pallipadi, Venkatesh
>Subject: Re: [BISECTED] EEE PC hangs when booting off battery
>
>On Tuesday 14 April 2009 09:17:28 am Arjan van de Ven wrote:
>> On Tue, 14 Apr 2009 08:59:01 -0600
>> Bjorn Helgaas <bjorn.helgaas@...com> wrote:
>>
>> > I can't help with the real problem of why the asynchronous battery
>> > init causes the hang.
>>
>> that got fixed already for the module case.
>
>But apparently still broken for the builtin case?  I think Alan is
>running pretty new bits -- he said "latest git" on April 11.
>
>> > But I do object to the magic makefile ordering change in that commit.
>> > Nobody reading the makefile can tell why battery is down at the end,
>> > and moving it apparently slows down boot significantly.
>>
>> for all cases I've seen it actually speeds it up, because the battery
>> now runs concurrently with the disk probe.
>
>I understand; I just meant that if somebody moves it back where it
>was, we'll mysteriously lose the speedup you got.  Maybe a comment
>in the makefile would be a short-term solution.
>
>> > So the
>> > ordering change just feels like a band-aid that covers up a place
>> > where ACPI could be improved.
>>
>> the reason for the move is that both the battery and other pieces take
>> the big acpi lock; which defeats the parallelism. So the battery needs
>> to happen at the end instead.
>
>Yep.  But I don't think it's anything about the Linux battery driver
>itself that makes it slow.  I think it's more likely that some of the
>ACPI methods it executes happen to be slow.  And that could afflict
>*any* driver, depending on the whim of a BIOS writer.
>
>My guess is that if we could run ACPI methods concurrently and avoid
>that big lock, the ordering wouldn't matter.  I know we probably can't
>do that any time soon, but I think it's good to make the problem
>visible at least with a "we need this magic order because ACPI doesn't
>support concurrent method execution" sort of comment.
>
>Bjorn
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