linux-kernel - Re: SATA kernel-buffered read VERY slow (not raid, Promise TX300 card); 2.6.23.1(vanilla)

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Date:	Tue, 1 Jan 2008 01:58:12 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Linda Walsh <lkml@...nx.org>
Cc:	Robert Hancock <hancockr@...w.ca>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: SATA kernel-buffered read VERY slow (not raid, Promise TX300
 card); 2.6.23.1(vanilla)

> rate began falling and at 128k block-reads-at-a-time or larger, it drops 
> below
> 20MB/s (again, only on buffered SATA).   It's hard to imagine what would
> slow down buffered SATA reads but not ATA and SCSI reads of the same
> size.  I'm using the 'cfq' scheduler with everything running at default

Try disabling NCQ - see if you've got a drive with the 'NCQ = no
readahead' flaw.

> priorities, but again, why only SATA slowness?  It seems that at the driver
> level, using direct reads, the SATA disk has the highest read rate (near
> 80MB/s). 

Beats me - something is wrong that your setup triggers - could be
firmware funnies or Linux ones. 

>     The only way I could tell before was using hdparm to read the 
> parameters.
> Since that doesn't work, it's hard to tell if they are set correctly, 
> but given

hdparm supports identify to read modes on drives with libata. The one
thing you cannot do is force modes right now.

>     More importantly, how does one set parameters for acoustic and power
> saving parameters?  Some of my disks are used as 'backup' devices for my

hdparm or blktool

> other computers.  With the ATA disks, they were kept "spun down" when not
> being used (only used, 'normally', in early AM hours).

Well for backup devices you can use the fact SATA is hot/warm plug.

>     Another new "problem" (not as important) -- even though SATA disks are
> called with "sdX", my ATA disks that *were* at hda-hdc are now at hde-hdg.

NOTABUG - your BIOS has decided to move them from the legacy addresses so
they move from hda-d to e-g.

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