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Date: Fri, 1 Mar 2002 16:51:04 -0800
From: Mike Anderson <andmike@us.ibm.com>
To: "Jeff V. Merkey" <jmerkey@vger.timpanogas.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: queue_nr_requests needs to be selective
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In-Reply-To: <20020301132254.A11528@vger.timpanogas.org>; from jmerkey@vger.timpanogas.org on Fri, Mar 01, 2002 at 01:22:54PM -0700
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Jeff V. Merkey [jmerkey@vger.timpanogas.org] wrote:
> 
> ..snip..
>
> What is really needed here is to allow queue_nr_requests to be 
> configurable on a per adapter/device basis for these high end 
> raid cards like 3Ware since in a RAID 0 configuration, 8 drives
> are in essence a terabyte (1.3 terrabytes in our configuration) 
> and each adapter is showing up as a 1.3 TB device.  64/128
> requests are simply not enough to get the full spectrum of 
> performance atainable with these cards.
> 
Not having direct experience on this card it appears that increasing the
queue_nr_requests number will not allow you to have more ios in flight.

Unless I am reading the driver wrong you will be limited to
TW_MAX_CMDS_PER_LUN (15). This value is used by scsi_build_commandblocks
to allocate scsi commands for your scsi_device. This driver does not provide
a select_queue_depths function which allows for increase to the default
template value. 

Could it be that the experimentation of increasing this number has
allowed for better merging.

-Mike
-- 
Michael Anderson
andmike@us.ibm.com

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