Re: [PATCH v7] NVMe: conversion to blk-mq

Jens Axboe
2014-06-10T21:15:38Z

On 06/10/2014 03:10 PM, Keith Busch wrote:
> On Tue, 10 Jun 2014, Jens Axboe wrote:
>> On 06/10/2014 01:29 PM, Keith Busch wrote:
>>> I have two devices, one formatted 4k, the other 512. The 4k is used as
>>> the TEST_DEV and 512 is used as SCRATCH_DEV. I'm always hitting a BUG
>>> when
>>> unmounting the scratch dev in xfstests generic/068. The bug looks like
>>> nvme was trying to use an SGL that doesn't map correctly to a PRP.
>>
>> I'm guessing it's some of the coalescing settings, since the driver is
>> now using the generic block rq mapping.
>
> Ok, sounds right. I mentioned in a way earlier review it doesn't look
> like a request that doesn't conform to a PRP list would get split anymore,
> and this test seems to confirm that.
>
> Can we create something that will allow a driver to add DMA constraints to
> a request queue with the rules of a PRP list?

I haven't even looked at the rules - can you briefly outline them? From
a quick look, seems it does prp chaining for every 512 entries. But
nvme_setup_prps() looks like voodoo to an uninitiated, it could have
used a comment or two :-)