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

Suganath Prabu Subramani
2017-08-09T12:37:16Z

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@oracle.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