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Tue, 8 Dec 2020 22:37:17 +0000 (GMT) Subject: Re: [PATCH v2 01/17] ibmvfc: add vhost fields and defaults for MQ enablement To: Hannes Reinecke , Brian King , james.bottomley@hansenpartnership.com Cc: martin.petersen@oracle.com, linux-scsi@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, brking@linux.ibm.com References: <20201202005329.4538-1-tyreld@linux.ibm.com> <20201202005329.4538-2-tyreld@linux.ibm.com> <38903a4f-9253-0b4b-6f67-af78ec86175f@linux.ibm.com> <6ce79011-d288-7a49-3d51-262da58d8486@suse.de> From: Tyrel Datwyler Message-ID: Date: Tue, 8 Dec 2020 14:37:16 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <6ce79011-d288-7a49-3d51-262da58d8486@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2020-12-08_15:2020-12-08,2020-12-08 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 spamscore=0 suspectscore=0 impostorscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 bulkscore=0 phishscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012080137 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/7/20 3:56 AM, Hannes Reinecke wrote: > On 12/4/20 3:26 PM, Brian King wrote: >> On 12/2/20 11:27 AM, Tyrel Datwyler wrote: >>> On 12/2/20 7:14 AM, Brian King wrote: >>>> On 12/1/20 6:53 PM, Tyrel Datwyler wrote: >>>>> Introduce several new vhost fields for managing MQ state of the adapter >>>>> as well as initial defaults for MQ enablement. >>>>> >>>>> Signed-off-by: Tyrel Datwyler >>>>> --- >>>>>   drivers/scsi/ibmvscsi/ibmvfc.c |  9 ++++++++- >>>>>   drivers/scsi/ibmvscsi/ibmvfc.h | 13 +++++++++++-- >>>>>   2 files changed, 19 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c >>>>> index 42e4d35e0d35..f1d677a7423d 100644 >>>>> --- a/drivers/scsi/ibmvscsi/ibmvfc.c >>>>> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c >>>>> @@ -5161,12 +5161,13 @@ static int ibmvfc_probe(struct vio_dev *vdev, const >>>>> struct vio_device_id *id) >>>>>       } >>>>>         shost->transportt = ibmvfc_transport_template; >>>>> -    shost->can_queue = max_requests; >>>>> +    shost->can_queue = (max_requests / IBMVFC_SCSI_HW_QUEUES); >>>> >>>> This doesn't look right. can_queue is the SCSI host queue depth, not the MQ >>>> queue depth. >>> >>> Our max_requests is the total number commands allowed across all queues. From >>> what I understand is can_queue is the total number of commands in flight allowed >>> for each hw queue. >>> >>>          /* >>>           * In scsi-mq mode, the number of hardware queues supported by the LLD. >>>           * >>>           * Note: it is assumed that each hardware queue has a queue depth of >>>           * can_queue. In other words, the total queue depth per host >>>           * is nr_hw_queues * can_queue. However, for when host_tagset is set, >>>           * the total queue depth is can_queue. >>>           */ >>> >>> We currently don't use the host wide shared tagset. >> >> Ok. I missed that bit... In that case, since we allocate by default only 100 >> event structs. If we slice that across IBMVFC_SCSI_HW_QUEUES (16) queues, then >> we end up with only about 6 commands that can be outstanding per queue, >> which is going to really hurt performance... I'd suggest bumping up >> IBMVFC_MAX_REQUESTS_DEFAULT from 100 to 1000 as a starting point. >> > Before doing that I'd rather use the host-wide shared tagset. > Increasing the number of requests will increase the memory footprint of the > driver (as each request will be statically allocated). > In the case where we use host-wide how do I determine the queue depth per hardware queue? Is is hypothetically can_queue or is it (can_queue / nr_hw_queues)? We want to allocate an event pool per-queue which made sense without host-wide tags since the queue depth per hw queue is exactly can_queue. -Tyrel