linux-kernel - Re: [PATCH RESEND v11 0/4] block layer runtime pm

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Date:	Fri, 22 Mar 2013 09:09:58 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Aaron Lu <aaron.lu@...el.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Tejun Heo <tj@...nel.org>, linux-pm@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, Aaron Lu <aaron.lwe@...il.com>,
	Shane Huang <shane.huang@....com>,
	Oliver Neukum <oneukum@...e.de>
Subject: Re: [PATCH RESEND v11 0/4] block layer runtime pm

On Fri, Mar 15 2013, Aaron Lu wrote:
> In August 2010, Jens and Alan discussed about "Runtime PM and the block
> layer". http://marc.info/?t=128259108400001&r=1&w=2
> And then Alan has given a detailed implementation guide:
> http://marc.info/?l=linux-scsi&m=133727953625963&w=2
> 
> To test:
> # ls -l /sys/block/sda
> /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda
> 
> # echo 10000 > /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/power/autosuspend_delay_ms
> # echo auto > /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/power/control
> Then you'll see sda is suspended after 10secs idle.
> 
> [ 1767.680192] sd 2:0:0:0: [sda] Synchronizing SCSI cache
> [ 1767.680317] sd 2:0:0:0: [sda] Stopping disk
> 
> And if you do some IO, it will resume immediately.
> [ 1791.052438] sd 2:0:0:0: [sda] Starting disk
> 
> For test, I often set the autosuspend time to 1 second. If you are using
> a GUI, the 10 seconds delay may be too long that the disk can not enter
> runtime suspended state.
> 
> Note that sd's runtime suspend callback will dump some kernel messages
> and the syslog daemon will write kernel message to /var/log/messages,
> making the disk instantly resume after suspended. So for test, the
> syslog daemon should better be temporarily stopped.
> 
> A git repo for it, on top of v3.9-rc1:
> https://github.com/aaronlu/linux.git blockpm

I think it's about time we get this in, but the patchset isn't very
friendly from a scsi vs block perspective. Can you re-shuffle the REQ_PM
change, just do a separate patch for that. I'll get it queued up for
3.10 then.

-- 
Jens Axboe

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