From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: calling scsi_adjust_queue_depth() during I/O... Date: Fri, 05 Aug 2005 12:20:31 -0500 Message-ID: <1123262432.5003.44.camel@mulgrave> References: <20050804234155.GJ13374@plap.qlogic.org> <20050805075751.GN9369@suse.de> <20050805110911.GA22867@htj.dyndns.org> <42F350E6.2090109@gmail.com> <20050805123301.GA3311@htj.dyndns.org> <1123259528.5003.36.camel@mulgrave> <20050805171034.GA5046@htj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from stat16.steeleye.com ([209.192.50.48]:46031 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S263087AbVHERUs (ORCPT ); Fri, 5 Aug 2005 13:20:48 -0400 In-Reply-To: <20050805171034.GA5046@htj.dyndns.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Tejun Heo Cc: Jens Axboe , Andrew Vasquez , Linux-SCSI Mailing List On Sat, 2005-08-06 at 02:10 +0900, Tejun Heo wrote: > Yes, we can do that, but I'm not sure if that would be necessary. > AFAIK, queues are normally not very deep and a tag only occupies one > pointer and one bit. Also, the shrinking operation isn't very common, > at least for traditional SPI devices and SATA drives, I think. > > Are newer SCSI devices (say, SAS/iSCSI) different? - like having very > deep queue and needing dynamic queue depth adjustment? If that's the > case, I think I can implement shrinking in a separate patch. (and try > not to screw up this time ;-) Well, yes, there are reasons for wanting deeper queues, but I'd leave it for the time being. What I'm looking into is support for aic7xxx/aic79xx queueing. There, the sequencer has to have a globally unique tag (from which it generates the device locally unique tag internally). That gives TCQ depths of up to 512 I believe. However, still probably not a significant waste of memory to worry about. James