linux-kernel - Re:Re: [PATCH] make blk_mq_map_queues more friendly for cpu topology

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Date:   Wed, 27 Mar 2019 17:17:18 +0800 (CST)
From:   luferry <luferry@....com>
To:     "Christoph Hellwig" <hch@....de>
Cc:     "Jens Axboe" <axboe@...nel.dk>,
        "Dongli Zhang" <dongli.zhang@...cle.com>,
        "Ming Lei" <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH] make blk_mq_map_queues more friendly for cpu
 topology




Actually,  I just bought one vm from public cloud provider and run into this problem.
after reading code and compare pci device info, I reproduce this scenario.

Since common users cannot change msi vector numbers, so I suggest blk_mq_map_queues to be 
more friendly. blk_mq_map_queues may be the  last choice. 





At 2019-03-27 16:16:19, "Christoph Hellwig" <hch@....de> wrote:
>On Tue, Mar 26, 2019 at 03:55:10PM +0800, luferry wrote:
>> 
>> 
>> 
>> At 2019-03-26 15:39:54, "Christoph Hellwig" <hch@....de> wrote:
>> >Why isn't this using the automatic PCI-level affinity assignment to
>> >start with?
>> 
>> When enable virtio-blk with multi queues but with only 2 msix-vector.
>> vp_dev->per_vq_vectors will be false, vp_get_vq_affintity will return NULL directly
>> so blk_mq_virtio_map_queues will fallback to blk_mq_map_queues.
>
>What is the point of the multiqueue mode if you don't have enough
>(virtual) MSI-X vectors?