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Petersen" Organization: Oracle Corporation References: <20200211122821.GA29811@ming.t460p> Date: Wed, 12 Feb 2020 22:02:08 -0500 In-Reply-To: (Damien Le Moal's message of "Wed, 12 Feb 2020 01:47:53 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1.92 (gnu/linux) MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9529 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 suspectscore=0 spamscore=0 adultscore=0 bulkscore=0 phishscore=0 malwarescore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002130023 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9529 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxscore=0 malwarescore=0 suspectscore=0 mlxlogscore=999 priorityscore=1501 clxscore=1011 impostorscore=0 lowpriorityscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002130023 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200212_190217_886202_373C083D X-CRM114-Status: GOOD ( 18.00 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-block@vger.kernel.org" , "linux-nvme@lists.infradead.org" , Tim Walker , linux-scsi , Ming Lei Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org Damien, > Exposing an HDD through multiple-queues each with a high queue depth > is simply asking for troubles. Commands will end up spending so much > time sitting in the queues that they will timeout. Yep! > This can already be observed with the smartpqi SAS HBA which exposes > single drives as multiqueue block devices with high queue depth. > Exercising these drives heavily leads to thousands of commands being > queued and to timeouts. It is fairly easy to trigger this without a > manual change to the QD. This is on my to-do list of fixes for some > time now (lacking time to do it). Controllers that queue internally are very susceptible to application or filesystem timeouts when drives are struggling to keep up. > NVMe HDDs need to have an interface setup that match their speed, that > is, something like a SAS interface: *single* queue pair with a max QD > of 256 or less depending on what the drive can take. Their is no > TASK_SET_FULL notification on NVMe, so throttling has to come from the > max QD of the SQ, which the drive will advertise to the host. At the very minimum we'll need low queue depths. But I have my doubts whether we can make this work well enough without some kind of TASK SET FULL style AER to throttle the I/O. > NVMe specs will need an update to have a "NONROT" (non-rotational) bit in > the identify data for all this to fit well in the current stack. Absolutely. -- Martin K. Petersen Oracle Linux Engineering _______________________________________________ linux-nvme mailing list linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme