linux-kernel - Re: echo mem > /sys/power/state

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Date:	Fri, 18 Jan 2008 09:51:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Zan Lynx <zlynx@....org>, Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <lenb@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: echo mem > /sys/power/state

* Jiri Slaby <jirislaby@...il.com> wrote:

> On 01/17/2008 08:13 PM, Andrew Morton wrote:
>> On Thu, 17 Jan 2008 10:36:51 -0700 Zan Lynx <zlynx@....org> wrote:
>>> Heh.  Laptop suspend to anything has been so broken for so long in the
>>> -mm series on my Compaq R3000 that I didn't even know it was ever
>>> supposed to work.
>>
>> It gets broken more often than anything else.  I do test each release on
>> two laptops and I get to do a lot of bisection searching and
>> grumpygramming as a result.
>>
>> Probably it would be more efficient to have the people who wrote the code
>> also test it.
>
> Big fat ACK from here. Suspend issues in past few -mms were *very* 
> hard (and time consuming) to track down.

it's really all a matter of reducing latencies. Testing suspend/resume 
is manual work currently (it either needs me hit a key on the laptop or 
necessiates the use of a test-script that might or might not work 
depending on whether the new /dev/rtc driver is enabled). So few people 
besides those that rely on it will do it. The more a patch that breaks 
suspend is out in the open unidentified, the more damage it does: it 
gets into more trees, gets harder to bisect, etc.

So please give us overworked maintainers an easy to use .config option 
dependent on CONFIG_DEBUG_KERNEL=y that automatically triggers a simple 
suspend+resume sequence 60 seconds after bootup. It would be godsent. 
(dont worry about proper gx resume) I compile and boot up every patch i 
add to x86.git, so this would catch crap the moment we add it to the 
tree.

The other, more long-term trick is to make rarely used functionality 
more widely used. Consolidate code. Try to merge as much of 
suspend/resume with bootup/module-insert/shutdown sequences as possible. 
Suspend unused devices more agressively - such as non-mounted block 
devices or downed networking ports. Try create more network effects with 
other functionality, suspend and resume is not just about suspending 
laptops, it can/could be used for so much more stuff. Try to get Pavel's 
"Sleepy Linux" concept to work reasonably well - so that more people 
(including developers) would use it in a daily basis.

Test coverage of a given piece of code is a direct function of its 
utility and of its ease of testing. Decreeing "this is important" really 
wont get more testing done. What you should realize i think is that this 
is not a social/mindset problem (so no need to get frustrated about it), 
this is a mostly technology problem: you can gradually _code_ your way 
into people's test efforts.

	Ingo
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