linux-kernel - Re: [RFC PATCH 2/2] block: virtio-blk: support multi virt queues per virtio-blk device

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Date:	Wed, 18 Jun 2014 00:00:07 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Stefan Hajnoczi <stefanha@...il.com>, Jens Axboe <axboe@...nel.dk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>, linux-api@...r.kernel.org,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [RFC PATCH 2/2] block: virtio-blk: support multi virt queues per
 virtio-blk device

On Tue, Jun 17, 2014 at 11:53 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> Il 17/06/2014 17:50, Ming Lei ha scritto:
>
>>> > It would be nice to allocate virtqueues dynamically instead of
>>> > hardcoding the limit.  virtio-scsi also allocates virtqueues
>>> > dynamically.
>>
>> virtio-scsi may have lots of LUN, but virtio-blk only has one disk
>> which needn't lots of hardware queues.
>
>
> If you want to do queue steering based on the guest VCPU number, the number
> of queues must be = to the number of VCPUs shouldn't it?
>
> I tried using a divisor of the number of VCPUs, but couldn't get the block
> layer to deliver interrupts to the right VCPU.

For blk-mq's hardware queue, that won't be necessary to equal to
VCPUs number, and irq affinity per hw queue can be simply set as
blk_mq_hw_ctx->cpumask.

Thanks,
--
Ming Lei
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