linux-kernel - Re: [patch 2/4] Expose Power Management Policy option to users

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Date:	Wed, 01 Aug 2007 03:02:55 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Kristen Carlson Accardi <kristen.c.accardi@...el.com>
CC:	Jeff Garzik <jeff@...zik.org>, James.Bottomley@...eleye.com,
	linux-scsi@...r.kernel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	edwintorok@...il.com, axboe@...nel.dk
Subject: Re: [patch 2/4] Expose Power Management Policy option to users

Kristen Carlson Accardi wrote:
> I think what you are saying is that you'd like a way to use your HIPM
> and DIPM without ALPM on the AHCI driver.  Fine - it's really easy
> to add these levels later - if they don't make sense at the sysfs interface
> we can add module params to specify the definition of "min_power" as 
> being performed via HIPM and DIPM instead of ALPM - although as of yet we
> have no evidence what so ever that this method actually adds value over
> ALPM.

I don't really care whose PS implementation goes in.  Believe me.  I try
to stay away from that.  I don't even like my previous implementation.

ALPM has unnecessary performance penalty && is not applicable to
non-ahci controller.  Have you tested ALPM on non-intel ahcis?  There
are a lot out there these days.

I don't think the interface you're suggesting is a good one.  Do you?

>> Also, I generally don't think AHCI ALPM is a good idea.  It doesn't have
>> 'cool down' period before entering PS state which unnecessarily hampers
>> performance and might increase chance of device malfunction.
> 
> "might increase"?  How about some actual examples of where you've shown
> this to be a problem?

I wouldn't have used "might" if I had actual examples.  Well, feel free
to disregard anything following the "might".  I just feel uneasy about
jumping back and forth between PS and active states between consecutive
commands.

> I can assert that I think ALPM is a good idea,
> because I've never had a report of it causing problems.  Windows has 
> been using this feature for a very long time - and you have to admit that
> they have a pretty large market share.  Nobody is complaining about ALPM
> increasing device malfunction, so unless you have proof it seems insane
> to nak due to this. 

Is ALPM enabled by default?  How do they deal with the performance
degradation?

-- 
tejun
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