linux-kernel - Re: [PATCH v3 03/13] mpt3sas: SGL to PRP Translation for I/Os to NVMe devices

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Date:   Tue, 08 Aug 2017 12:12:13 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Suganath Prabu S <suganath-prabu.subramani@...adcom.com>
Cc:     JBottomley@...allels.com, jejb@...nel.org, hch@...radead.org,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        Sathya.Prakash@...adcom.com, kashyap.desai@...adcom.com,
        linux-kernel@...r.kernel.org, chaitra.basappa@...adcom.com,
        sreekanth.reddy@...adcom.com, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v3 03/13] mpt3sas: SGL to PRP Translation for I/Os to NVMe  devices


Suganath,

> +	/*
> +	 ** Below code detects gaps/holes in IO data buffers.
> +	 ** What does holes/gaps mean?
> +	 ** Any SGE except first one in a SGL starts at non NVME page size
> +	 ** aligned address OR Any SGE except last one in a SGL ends at
> +	 ** non NVME page size boundary.
> +	 **
> +	 ** Driver has already informed block layer by setting boundary rules
> +	 ** for bio merging done at NVME page size boundary calling kernel API
> +	 ** blk_queue_virt_boundary inside slave_config.
> +	 ** Still there is possibility of IO coming with holes to driver because
> +	 ** of IO merging done by IO scheduler.

All this SGL to PRP code needs to go.

If you are seeing anything that's not a valid PRP after setting the
queue virt boundary then there's a block layer bug that needs to be
debugged and fixed. Regardless of whether you are using an I/O scheduler
or not.

-- 
Martin K. Petersen	Oracle Linux Engineering