linux-kernel - Re: [PATCH RFC v1 0/5] Add SCSI per device tagsets

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Message-ID: <9e7925d6-067c-0b3a-a788-f036272496e6@huawei.com>
Date:   Mon, 21 Feb 2022 17:40:23 +0000
From:   John Garry <john.garry@...wei.com>
To:     "Melanie Plageman (Microsoft)" <melanieplageman@...il.com>,
        <mikelley@...rosoft.com>, <jejb@...ux.ibm.com>,
        <kys@...rosoft.com>, <martin.petersen@...cle.com>,
        <mst@...hat.com>, <benh@...nel.crashing.org>,
        <decui@...rosoft.com>, <don.brace@...rochip.com>,
        <R-QLogic-Storage-Upstream@...vell.com>, <haiyangz@...rosoft.com>,
        <jasowang@...hat.com>, <kashyap.desai@...adcom.com>,
        <mpe@...erman.id.au>, <njavali@...vell.com>, <pbonzini@...hat.com>,
        <paulus@...ba.org>, <sathya.prakash@...adcom.com>,
        <shivasharan.srikanteshwara@...adcom.com>,
        <sreekanth.reddy@...adcom.com>, <stefanha@...hat.com>,
        <sthemmin@...rosoft.com>, <suganath-prabu.subramani@...adcom.com>,
        <sumit.saxena@...adcom.com>, <tyreld@...ux.ibm.com>,
        <wei.liu@...nel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <megaraidlinux.pdl@...adcom.com>,
        <mpi3mr-linuxdrv.pdl@...adcom.com>, <storagedev@...rochip.com>,
        <virtualization@...ts.linux-foundation.org>,
        <linux-hyperv@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-scsi@...r.kernel.org>, <MPT-FusionLinux.pdl@...adcom.com>
CC:     <andres@...razel.de>
Subject: Re: [PATCH RFC v1 0/5] Add SCSI per device tagsets

On 18/02/2022 18:41, Melanie Plageman (Microsoft) wrote:
> For example: a device provisioned with high IOPS and BW limits on the same
> controller as a smaller and slower device can starve the slower device of tags.
> This is especially noticeable when the slower device's workload has low I/O
> depth tasks.

If you check hctx_may_queue() in the block code then it is noticeable 
that a fair allocation of HW queue depth is allocated per request queue 
to ensure we don't get starvation.

Thanks,
John