From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH V7 4/5] virtio-scsi: introduce multiqueue support
Date: Mon, 25 Mar 2013 15:27:30 +0100
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To: Bart Van Assche <bvanassche@acm.org>
Cc: kvm@vger.kernel.org, linux-scsi@vger.kernel.org, mst@redhat.com, linux-kernel@vger.kernel.org, JBottomley@parallels.com, virtualization@lists.linux-foundation.org
List-Id: linux-scsi@vger.kernel.org

Il 25/03/2013 08:25, Bart Van Assche ha scritto:
>>
>> +        queue_num = smp_processor_id();
>> +        while (unlikely(queue_num >= vscsi->num_queues))
>> +            queue_num -= vscsi->num_queues;
>> +
>> +        tgt->req_vq = vq = &vscsi->req_vqs[queue_num];
>> +    }
>> +
>> +    spin_unlock_irqrestore(&tgt->tgt_lock, flags);
>> +    return vq;
>> +}
> 
> Is there any reason why the smp_processor_id() % vscsi->num_queues
> computation in virtscsi_pick_vq() has been implemented as a loop instead
> of as an arithmetic operation ? If so, I would appreciate it if that
> could be explained in a comment.

The expectation is that vscsi->num_queues is the same as the number of
CPUs in the virtual machine; see patch 5 too.

Paolo