linux-kernel - Re: [PATCH -next] blk-mq: fix boot time regression for scsi drives with multiple hctx

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Message-ID: <Yql6gbP2NmKsvFqH@infradead.org>
Date:   Tue, 14 Jun 2022 23:21:53 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     Ming Lei <ming.lei@...hat.com>, axboe@...nel.dk,
        djeffery@...hat.com, bvanassche@....org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next] blk-mq: fix boot time regression for scsi drives
 with multiple hctx

On Tue, Jun 14, 2022 at 09:15:36PM +0800, Yu Kuai wrote:
> > for making so long, so I guess there must be other delay added by the feature
> > of BLK_MQ_F_TAG_HCTX_SHARED.
> 
> Please see details in the reasons 2), scsi scan will call
> __scsi_remove_device() a lot of times(each host, each channel, each
> target).

Well, if the SCSI core does that you are falling back to a sequentical
scan instad of using REPORT LUNS.  Which seems like a bug on its own
that is worth investigation.