linux-kernel - Re: [RFC v2 PATCH 2/4] block: add queue runtime pm callbacks

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Date:	Thu, 24 May 2012 10:52:35 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lin Ming <ming.m.lin@...el.com>
cc:	Jens Axboe <axboe@...nel.dk>, Jeff Moyer <jmoyer@...hat.com>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<linux-scsi@...r.kernel.org>
Subject: Re: [RFC v2 PATCH 2/4] block: add queue runtime pm callbacks

On Thu, 24 May 2012, Lin Ming wrote:

> > When tested the patches, I found that kjournald and flusher thread
> > frequently resume the disk.
> 
> Just found that it's because "printk".
> 
> When disk is suspended, it prints out some message, for example,
> 
> [  670.597103] sd 0:0:0:0: [sda] Synchronizing SCSI cache
> [  670.597827] sd 0:0:0:0: [sda] Stopping disk
> 
> Then syslogd is waken up to write the log.
> So disk is resumed right after suspended.

:-)  Very amusing!  So if you change those two messages in sd_suspend
(and maybe also the message in sd_resume) from KERN_NOTICE to
KERN_DEBUG, things ought to improve.

Alan Stern

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