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

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Date:   Wed, 9 Aug 2017 18:07:13 +0530
From:   Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     "JBottomley@...allels.com" <JBottomley@...allels.com>,
        jejb@...nel.org, Christoph Hellwig <hch@...radead.org>,
        linux-scsi@...r.kernel.org,
        Sathya Prakash <Sathya.Prakash@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        linux-kernel@...r.kernel.org,
        Chaitra Basappa <chaitra.basappa@...adcom.com>,
        Sreekanth Reddy <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

Hi Martin,
This code was added to detect holes, when we started testing with 4.9
kernel. when we disabled "use_blk_mq" and no merges, we are hitting
issues with holes. Anyhow In latest upstream, it got fixed with this
commit 5a8d75a1b8c99bdc926ba69b7b7dbe4fae81a5af

So we are removing the code related to hole detection .

Thanks,
Suganath Prabu S



On Tue, Aug 8, 2017 at 9:42 PM, Martin K. Petersen
<martin.petersen@...cle.com> wrote:
>
> 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