From: Mike Christie <michaelc@cs.wisc.edu>
To: john clyne <clyne@ucar.edu>
Cc: linux-scsi@vger.kernel.org
Subject: Re: IO transfer limits
Date: Wed, 10 Jan 2007 11:40:30 -0600 [thread overview]
Message-ID: <45A5250E.3020205@cs.wisc.edu> (raw)
In-Reply-To: <8260533.post@talk.nabble.com>
john clyne wrote:
> Can anyone give me some guidance on where in the IO stack I might be running
> into a 512KB limit on IO transfer sizes to an external FC device? I've
> checked IO scheduler parameter
> (/sys/block/<dev>/queue/{max_sectors_kb,max_hw_sectors_kb}. Both are set to
> 32767. I'm using Qlogic HBAs (qla2312), but I don't see any relevent
> parameters. I'm running RHEL 4.0 with a 2.6.9-34 kernel. Any pointers would
> be greatly appreciated.
>
There are also scatterlist limits.
/sys/class/scsi_host/hostX/sg_tablesize is a limit for the number of
scatter list entries. For qla2xxx it is 255.
The scsi layer sets the queue's max_phys_segments to 128 by default. I
thought there was ia scsi compile time option to increase this, but
maybe you have to just modify the SCSI_MAX_PHYS_SEGMENTS define by hand.
So with the default value and with 4 K pages if you end up getting pages
that cannot be clustered you will end up with 4K * 128.
next prev parent reply other threads:[~2007-01-10 17:40 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-10 16:16 IO transfer limits john clyne
2007-01-10 17:40 ` Mike Christie [this message]
2007-01-10 23:47 ` john clyne
2007-01-11 1:15 ` Douglas Gilbert
2007-01-11 16:13 ` Stefan Richter
2007-01-11 21:50 ` Douglas Gilbert
2007-01-12 0:54 ` Stefan Richter
2007-01-12 22:27 ` john clyne
2007-01-10 18:38 ` Douglas Gilbert
2007-01-10 23:07 ` john clyne
2007-01-11 18:23 ` James Bottomley
2007-01-11 19:48 ` john clyne
2007-01-12 1:17 ` James Bottomley
2007-01-11 19:23 ` no utility / method to show association between host bus adapter and non-sg BLOCK devices Thayne Harmon
2007-01-11 20:15 ` Douglas Gilbert
[not found] ` <45AE22E0.DB3A.00B8.0@novell.com>
2007-01-17 21:04 ` no utility / method to show association between HBA & non-sg BLOCK (scsi) devices - register_blkdev() Douglas Gilbert
2007-01-17 22:06 ` Andrew Patterson
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