Message-ID: <4647AF0E.7030700@tmr.com>
Date: Sun, 13 May 2007 20:36:30 -0400
From: Bill Davidsen <davidsen@tmr.com>
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To: "Rafael J. Wysocki" <rjw@sisk.pl>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
       Coywolf Qi Hunt <coywolf@gmail.com>, Len Brown <lenb@kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Alexey Starikovskiy <alexey_y_starikovskiy@linux.intel.com>,
       LKML <linux-kernel@vger.kernel.org>, Pavel Machek <pavel@ucw.cz>,
       linux-acpi@vger.kernel.org, Stefan Seyfried <seife@suse.de>
Subject: Re: [PATCH] swsusp: Use platform mode by default
References: <200611011323.14830.rjw@sisk.pl> <200705111121.51704.rjw@sisk.pl> <alpine.LFD.0.98.0705110912290.3986@woody.linux-foundation.org> <200705112208.53971.rjw@sisk.pl>
In-Reply-To: <200705112208.53971.rjw@sisk.pl>
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Rafael J. Wysocki wrote:
> On Friday, 11 May 2007 18:30, Linus Torvalds wrote:
>> On Fri, 11 May 2007, Rafael J. Wysocki wrote:
>>> We're working on fixing the breakage, but currently it's difficult, because
>>> none of my testboxes has problems with the 'platform' hibernation and I
>>> cannot reproduce the reported issues.
>> The rule for anything ACPI-related has been: no regressions.
>>
>> It doesn't matter if something fixes 10 boxes, if it breaks a single one, 
>> it's going to get reverted.
> 
> [Well, I think I should stop explaining decisions that weren't mine.  Yet, I
> feel responsible for patches that I sign-off.]
> 
> Just to clarify, the change in question isn't new.  It was introduced by the
> commit 9185cfa92507d07ac787bc73d06c42222eec7239 before 2.6.20, at Seife's
> request and with Pavel's acceptance.
> 
>> We had much too much of the "two steps forward, one step back" dance with 
>> ACPI a few years ago, which is the reason that rule got installed (and 
>> which is why it's ACPI-only: in some other subsystems we accept the fact 
>> that sometimes we don't know how to fix some hardware issue, but the new 
>> situation is at least better than the old one).
>>
>> I agree that it can be aggravating to know that you can fix a problem for 
>> some people, but then being limited by the fact that it breaks for others. 
>> But beign able to *rely* on something that used to work is just too 
>> important, and with ACPI, you can never make a good judgement of which way 
>> works better (since it really just depends on some random firmware issues 
>> that we have zero visibility into).
>>
>> Also, quite often, it may *seem* like something fixes more boxes than it 
>> breaks, but it's because people report *breakage* only, and then a few 
>> months later it turns out that it's exactly the other way around: now it's 
>> a hundred people who report breakage with the *new* code, and the reason 
>> people thought it fixed more than it broke was that the people for whom 
>> the old code worked fine obviously never reported it!
>>
>> So this is why "a single regression is considered more important than ten 
>> fixes" - because a single regressionr report tends to actually be just the 
>> first indication of a lot of people who simply haven't tested the new code 
>> yet! People for whom the old code is broken are more likely to test new 
>> things.
>>
>> So I'd just suggest changing the default back to PM_DISK_SHUTDOWN (but 
>> leave the "pm_ops->enter" testing in place - ie not reverting the other 
>> commits in the series).
> 
> The series actually preserves the 2.6.20/21 behavior.  By defaulting back to
> PM_DISK_SHUTDOWN, we'll cause some users for whom 2.6.20 and 2.6.21 work to
> report this change as a regression, so please let me avoid making this decision
> (I'm not the maintainer of the hibernation code after all).
> 
> The problem is that we don't know about regressions until somebody reports them
> and if that happens after two affected kernel releases, what should we do?
> 
I think that one of the reasons people (guilty) don't report problems 
with suspend and hibernate is that it's been a problem on and off and 
when it breaks people don't bother to chase it, they just don't use it 
unless it's critical, or they install suspend2.

I only suggest that if 'platform' is more correct use that, don't change 
it again. Then fix platform.

-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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