Re: [PATCH 3/4] scsi: sd: register request queue after sd_revalidate_disk is done

From: Hannes Reinecke <hare@suse.de>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org,
	"James E . J . Bottomley" <jejb@linux.ibm.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org,
	Sathya Prakash <sathya.prakash@broadcom.com>,
	Chaitra P B <chaitra.basappa@broadcom.com>,
	Suganath Prabu Subramani  <suganath-prabu.subramani@broadcom.com>,
	Kashyap Desai <kashyap.desai@broadcom.com>,
	Sumit Saxena <sumit.saxena@broadcom.com>,
	Shivasharan S <shivasharan.srikanteshwara@broadcom.com>,
	"Ewan D . Milne" <emilne@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	Bart Van Assche <bart.vanassche@wdc.com>
Subject: Re: [PATCH 3/4] scsi: sd: register request queue after sd_revalidate_disk is done
Date: Wed, 20 Nov 2019 10:59:08 +0100	[thread overview]
Message-ID: <a5e67097-9c56-6cc7-37bf-fb704bfd95b9@suse.de> (raw)
In-Reply-To: <20191118103117.978-4-ming.lei@redhat.com>

On 11/18/19 11:31 AM, Ming Lei wrote:
> Prepare for improving SSD performance in the following patch, which
> needs to read queue flag of QUEUE_FLAG_NONROT in IO path. So we have
> to freeze queue before changing this flag in sd_revalidate_disk().
> 
> However, queue freezing becomes quite slow after the queue is registered
> because RCU period is involved.
> 
> So delay registering queue after sd_revalidate_disk() is done for
> avoiding slow queue freezing which will be added to sd_revalidate_disk()
> in the following patch.
> 
> Cc: Sathya Prakash <sathya.prakash@broadcom.com>
> Cc: Chaitra P B <chaitra.basappa@broadcom.com>
> Cc: Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>
> Cc: Kashyap Desai <kashyap.desai@broadcom.com>
> Cc: Sumit Saxena <sumit.saxena@broadcom.com>
> Cc: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
> Cc: Ewan D. Milne <emilne@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>,
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Bart Van Assche <bart.vanassche@wdc.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/scsi/sd.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 03163ac5fe95..0744c34468e1 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -3368,12 +3368,14 @@ static int sd_probe(struct device *dev)
>  	}
>  
>  	blk_pm_runtime_init(sdp->request_queue, dev);
> -	device_add_disk(dev, gd, NULL);
> +	device_add_disk_no_queue_reg(dev, gd);
>  	if (sdkp->capacity)
>  		sd_dif_config_host(sdkp);
>  
>  	sd_revalidate_disk(gd);
>  
> +	blk_register_queue(gd);
> +
>  	if (sdkp->security) {
>  		sdkp->opal_dev = init_opal_dev(sdp, &sd_sec_submit);
>  		if (sdkp->opal_dev)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      Teamlead Storage & Networking
hare@suse.de			                  +49 911 74053 688
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