linux-kernel - Re: [PATCH 3/8] cciss: change number of commands per controller

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Message-ID: <20061102143945.GM13555@kernel.dk>
Date:	Thu, 2 Nov 2006 15:39:45 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Mike Miller (OS Dev)" <mikem@...rdog.cca.cpqcorp.net>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 3/8] cciss: change number of commands per controller

On Thu, Nov 02 2006, Mike Miller (OS Dev) wrote:
> On Thu, Nov 02, 2006 at 03:11:50PM +0100, Jens Axboe wrote:
> > On Wed, Nov 01 2006, Mike Miller (OS Dev) wrote:
> > > +	{0x3211103C, "Smart Array E200i", &SA5_access, 120},
> > 
> > Is it 120, or 128? And how big is the allocated command array now, with
> > 512 commands?
> 
> The controller can handle up to 128, but I artificially limited it to 120
> for reasons I shouldn't discuss in public. :)

:-)

> Each command is 548 bytes w/o scatter gather chaining. So 548 * 512 = 280576
> bytes for the command list. We've tested using 1024 commands with several
> Smart Array controllers and have not encountered issues. The reason for the
> increase is performance. The busier you can keep the controller the better
> it works.

So this:

       hba[i]->cmd_pool = (CommandList_struct *)
            pci_alloc_consistent(hba[i]->pdev,
                    NR_CMDS * sizeof(CommandList_struct),
                    &(hba[i]->cmd_pool_dhandle));

is getting pretty huge then (it was already, actually).

-- 
Jens Axboe

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