linux-kernel - Re: Laptop shock detection and harddisk protection

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Date:	Wed, 17 Sep 2008 17:21:01 +0200
From:	Elias Oltmanns <eo@...ensachen.de>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Tejun Heo <tj@...nel.org>,
	Shem Multinymous <multinymous@...il.com>,
	Thomas Renninger <trenn@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: Laptop shock detection and harddisk protection

Pavel Machek <pavel@...e.cz> wrote:
> Hi!
>
>> Short of a satisfying proposition regarding the questions raised, I just
>> want to add two things that would be nice to solve in the future one way
>> or another and should perhaps be taken into consideration from the
>> beginning:
>> 
>> 1. Disable polling completely when it isn't required: once the hd has
>>    spun down, there is no need to keep polling the sensors at all. Only
>>    when the first request requiring the hd to spin up arrives, the
>>    kernel needs to hold back for a short while to gather enough data
>>    from the sensors, so shock protection is up and running again.
>
> hdparm can already tell if disk is spinning or not. As userland is
> polling, already, that may be enough?

Yes, I know it *is* possible, I just think it may not be completely
trivial to get it right. The only way I can think of, right now, is some
sort of polling in the hdparm way, i.e. issuing a ATA_CMD_CHK_POWER from
time to time. The question is how we are to decide when and how often we
should poll for the current power state of the HD.

>
>> 2. Make shock protection interact nicely with suspend operations:
>>    currently, we are out of luck if anything should happen after
>>    processes have been frozen. This is particularly unfortunatel in the
>>    case of s2disk.
>
> I'd say that s2disk is similar to early boot... no protection there. 

Well, this is true for resume. However, I can't help thinking that we
may do better than that until the disk spins down, particularly while
writing the image to disk.

Regards,

Elias
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