From mboxrd@z Thu Jan 1 00:00:00 1970 From: scameron@beardog.cce.hp.com Subject: 16 commands per lun limitation bug? Date: Wed, 10 Feb 2010 14:19:16 -0600 Message-ID: <20100210201916.GK11649@beardog.cce.hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from g1t0027.austin.hp.com ([15.216.28.34]:25128 "EHLO g1t0027.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753977Ab0BJUQW (ORCPT ); Wed, 10 Feb 2010 15:16:22 -0500 Content-Disposition: inline Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org Cc: mike.miller@hp.com, james.bottomley@hansenpartnership.com, scameron@beardog.cce.hp.com We have seen the amount of commands per lun that are sent to low level scsi driver limited to 16 commands per lun, (seemingly artificially, well below our can_queue and cmd_per_lun limits of 1020) 2.6.29 does not exhibit this bad behavior. 2.6.30, 2.6.31, 2.6.32 (2.6.32.1 through 2.6.32.8) do exhibit this bad behavior 2.6.31-rc1 does not exhibit this bad behavior Testing was done with fio with this config file: [global] description=4096 byte random reads - ${CONFIG} readwrite=randread blocksize=4K ioengine=libaio softrandommap=1 direct=1 runtime=2000 time_based #ramp_time=10 thread filename=/dev/sdb [iodepth=128] stonewall iodepth=128 When the problem is present, we only see 16 commands per lun, when not present, we see 128 commands per lun. Anybody else seen this problem? Anybody know what caused the brokeness between 2.6.29 and 2.6.30, or what fixed this between 2.6.32 and 2.6.33-rc1? Hard for me to do a git bisect as the only hardware I have capable of exercising the test case is Smart Array, and hpsa didn't go in until 2.6.33-rc1. Would like to know if other hardware/drivers encounter this problem as well. -- steve