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

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Message-ID: <5397753B.2020009@fb.com>
Date:	Tue, 10 Jun 2014 15:14:35 -0600
From:	Jens Axboe <axboe@...com>
To:	Keith Busch <keith.busch@...el.com>
CC:	Matias Bjørling <m@...rling.me>,
	"willy@...ux.intel.com" <willy@...ux.intel.com>,
	"sbradshaw@...ron.com" <sbradshaw@...ron.com>,
	"tom.leiming@...il.com" <tom.leiming@...il.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Subject: Re: [PATCH v7] NVMe: conversion to blk-mq

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 :-)


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