linux-kernel - Re: [PATCH 0/2] Limit number of hw queues by nr_cpu

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Message-ID: <47e8d8bf-1820-5cb4-ac78-1bcd5ea26c49@kernel.dk>
Date:   Wed, 10 Apr 2019 08:18:50 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Dongli Zhang <dongli.zhang@...cle.com>, linux-scsi@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-block@...r.kernel.org
Cc:     mst@...hat.com, jasowang@...hat.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, cohuck@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Limit number of hw queues by nr_cpu_ids for
 virtio-blk and virtio-scsi

On 3/27/19 4:36 AM, Dongli Zhang wrote:
> When tag_set->nr_maps is 1, the block layer limits the number of hw queues
> by nr_cpu_ids. No matter how many hw queues are use by
> virtio-blk/virtio-scsi, as they both have (tag_set->nr_maps == 1), they
> can use at most nr_cpu_ids hw queues.
> 
> In addition, specifically for pci scenario, when the 'num-queues' specified
> by qemu is more than maxcpus, virtio-blk/virtio-scsi would not be able to
> allocate more than maxcpus vectors in order to have a vector for each
> queue. As a result, they fall back into MSI-X with one vector for config
> and one shared for queues.
> 
> Considering above reasons, this patch set limits the number of hw queues
> used by nr_cpu_ids for both virtio-blk and virtio-scsi.

I picked both up for 5.1.

-- 
Jens Axboe