From: Paolo Bonzini <pbonzini@redhat.com>
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
Subject: Re: [PATCH V7 4/5] virtio-scsi: introduce multiqueue support
Date: Mon, 25 Mar 2013 15:27:30 +0100 [thread overview]
Message-ID: <51505ED2.70208@redhat.com> (raw)
In-Reply-To: <514FFC06.9030703@acm.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
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>,
linux-scsi@vger.kernel.org, kvm@vger.kernel.org, mst@redhat.com,
linux-kernel@vger.kernel.org, JBottomley@parallels.com,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH V7 4/5] virtio-scsi: introduce multiqueue support
Date: Mon, 25 Mar 2013 15:27:30 +0100 [thread overview]
Message-ID: <51505ED2.70208@redhat.com> (raw)
In-Reply-To: <514FFC06.9030703@acm.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
next prev parent reply other threads:[~2013-03-25 14:27 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-23 11:28 [PATCH V7 0/5] virtio-scsi multiqueue Wanlong Gao
2013-03-23 11:28 ` Wanlong Gao
2013-03-23 11:28 ` [PATCH V7 1/5] virtio-scsi: redo allocation of target data Wanlong Gao
2013-03-23 11:28 ` Wanlong Gao
2013-03-23 11:28 ` [PATCH V7 2/5] virtio-scsi: pass struct virtio_scsi to virtqueue completion function Wanlong Gao
2013-03-23 11:28 ` Wanlong Gao
2013-03-23 11:28 ` [PATCH V7 3/5] virtio-scsi: push vq lock/unlock into virtscsi_vq_done Wanlong Gao
2013-03-23 11:28 ` Wanlong Gao
2013-03-23 11:28 ` [PATCH V7 4/5] virtio-scsi: introduce multiqueue support Wanlong Gao
2013-03-23 11:28 ` Wanlong Gao
2013-03-25 7:25 ` Bart Van Assche
2013-03-25 7:25 ` Bart Van Assche
2013-03-25 14:27 ` Paolo Bonzini [this message]
2013-03-25 14:27 ` Paolo Bonzini
2013-03-23 11:28 ` [PATCH V7 5/5] virtio-scsi: reset virtqueue affinity when doing cpu hotplug Wanlong Gao
2013-03-23 11:28 ` Wanlong Gao
2013-03-28 2:22 ` [PATCH V7 0/5] virtio-scsi multiqueue Wanlong Gao
2013-03-28 2:22 ` Wanlong Gao
2013-04-05 8:55 ` Wanlong Gao
2013-04-05 8:55 ` Wanlong Gao
2013-04-06 8:40 ` James Bottomley
2013-04-06 10:14 ` Wanlong Gao
2013-04-06 10:14 ` Wanlong Gao
2013-04-07 2:01 ` Asias He
2013-04-07 2:01 ` Asias He
2013-04-08 13:36 ` Rusty Russell
2013-04-08 13:36 ` Rusty Russell
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