linux-kernel - Re: [PATCH] aic94xx: Increase can_queue and cmds_per

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Message-Id: <1156965920.7701.13.camel@mulgrave.il.steeleye.com>
Date:	Wed, 30 Aug 2006 15:25:20 -0400
From:	James Bottomley <James.Bottomley@...elEye.com>
To:	ltuikov@...oo.com
Cc:	"Darrick J. Wong" <djwong@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org, Alexis Bruemmer <alexisb@...ibm.com>,
	Mike Anderson <andmike@...ibm.com>,
	Konrad Rzeszutek <konrad@...nok.org>
Subject: Re: [PATCH] aic94xx: Increase can_queue and cmds_per_lun

On Wed, 2006-08-30 at 12:04 -0700, Luben Tuikov wrote:
> > --- a/drivers/scsi/aic94xx/aic94xx_init.c
> > +++ b/drivers/scsi/aic94xx/aic94xx_init.c
> > @@ -71,7 +72,7 @@ static struct scsi_host_template aic94xx
> >       .change_queue_type      = sas_change_queue_type,
> >       .bios_param             = sas_bios_param,
> >       .can_queue              = 1,
> > -     .cmd_per_lun            = 1,
> > +     .cmd_per_lun            = 2,
> 
> Why 2?  Why not 3?  If you can set this to 3, then why not 4?
> But if you can set it to 4, why not 5?
> 
> This value should also be dynamically set, it should depend on
> the type of LU and it shouldn't be present in the host template.
> (But that's an architectural argument which leads nowhere on lsml.)

actually, cmd_per_lun is pretty much a vestigial variable.  It's used
for the initial queue depth before the driver decides to turn on TCQ.
Thus, since the non-tagged depth should always only be 1, the only
useful value to set it to is 1.

James


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