linux-kernel - Re: [PATCH] scsi: sd: Contribute to randomness when running rotational device

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Date:   Thu, 6 Sep 2018 18:42:10 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Xuewei Zhang <xueweiz@...gle.com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Ming Lei <ming.lei@...hat.com>, Hannes Reinecke <hare@...e.de>,
        Christoph Hellwig <hch@....de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Aditya Kali <adityakali@...gle.com>,
        Guenter Roeck <groeck@...omium.org>, maze@...gle.com
Subject: Re: [PATCH] scsi: sd: Contribute to randomness when running
 rotational device

On Thu, Sep 06, 2018 at 03:27:53PM -0700, Bart Van Assche wrote:
> 
> Although this patch looks fine to me, seeing this patch makes me wonder
> whether the default should be changed (QUEUE_FLAG_MQ_DEFAULT) instead of
> modifying the sd driver. Can anyone remind me why QUEUE_FLAG_MQ_DEFAULT does
> not include QUEUE_FLAG_ADD_RANDOM?

There was a discussion about a number of *years* ago; blk-mq has been
baking for a very long time.  In the early days of block_mq, the
overwhelming percentage of the users of blk-mq where those who were
using PCIe attached flash.  So when, I raised this question, the
argument was that SSD users have no entropy.  Which I agree with; but
now that blk-mq is the default, and hard drives are using blk-mq, it's
time for a patch like Xuewei's.

Cheers,

					- Ted