linux-kernel - RE: [PATCH v3 10/13] scsi: fnic: Add support for multiqueue (MQ) in fnic

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Date:   Thu, 16 Nov 2023 21:02:31 +0000
From:   "Karan Tilak Kumar (kartilak)" <kartilak@...co.com>
To:     John Garry <john.g.garry@...cle.com>,
        "Sesidhar Baddela (sebaddel)" <sebaddel@...co.com>
CC:     "Arulprabhu Ponnusamy (arulponn)" <arulponn@...co.com>,
        "Dhanraj Jhawar (djhawar)" <djhawar@...co.com>,
        "Gian Carlo Boffa (gcboffa)" <gcboffa@...co.com>,
        "Masa Kai (mkai2)" <mkai2@...co.com>,
        "Satish Kharat (satishkh)" <satishkh@...co.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hannes Reinecke <hare@...e.de>
Subject: RE: [PATCH v3 10/13] scsi: fnic: Add support for multiqueue (MQ) in
 fnic_main.c

On Thursday, November 16, 2023 8:33 AM, John Garry <john.g.garry@...cle.com> wrote:
>
> On 15/11/2023 23:20, Karan Tilak Kumar (kartilak) wrote:
> >>> +
> >>> +     if (intr_mode == VNIC_DEV_INTR_MODE_MSI || intr_mode == VNIC_DEV_INTR_MODE_INTX) {
> >>> +             FNIC_MAIN_DBG(KERN_ERR, fnic->lport->host, fnic->fnic_num,
> >>> +                     "intr_mode is not msix\n");
> >>                        Are these checks just paranoia? I mean that it is strange to have
> >>                        fnic_mq_map_queues_cpus() called but not be required to do anything.
> >>
> > Unified Computing Servers Management (UCSM) is a GUI tool to configure Cisco Servers.
> > There are interrupt options that can be modified to INTX or MSI or MSI-x.
> > All these options are still supported.
> >
> > However, we do not support multiqueue (MQ) on MSI or INTX.
>
> By this I assume it means nr_hw_queues = 1 for MSI or INTX

That's correct, John.

> > These checks are present to only prevent an MQ "misconfiguration".
>
> > If you check blk_mq_update_queue_map(), for set->ops->map_queues unset we call blk_mq_map_queues() - I am just wondering what does the equivalent to blk_mq_map_queues() for you in these other modes.
>
> > I am concerned that it is not proper that we have a set->ops->map_queues method, but it does nothing in some scenarios.
>
> I think we get away with this as mq_map[for all CPUs] is 0, which points to the only HW queue.

Yes, that's correct. This is what I found during testing as well.

Regards,
Karan