Re: [PATCHv2 1/3] block: introduce rq_list_for_each_safe macro

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 12/30/2021 5:30 PM, Keith Busch wrote:
> On Thu, Dec 30, 2021 at 04:38:57PM +0200, Max Gurtovoy wrote:
>> On 12/29/2021 10:57 PM, Keith Busch wrote:
>>> On Wed, Dec 29, 2021 at 06:39:02PM +0100, Christoph Hellwig wrote:
>>>> (except for the fact that it, just like the other rq_list helpers
>>>> really should go into blk-mq.h, where all request related bits moved
>>>> early in this cycle)
>>> Agreed, I just put it here because it's where the other macros live. But
>>> 'struct request' doesn't exist in this header, so it does seem out of
>>> place.  For v3, I'll add a preceding patch to move them all to blk-mq.h.
>> Did you see the discussion I had with Jens ?
> I did, yes. That's when I noticed the error handling wasn't right, and
> doing it correctly was a bit clunky. This series was supposed to make it
> easier for drivers to use the new interface.
>   
>> Seems it works only for non-shared tagsets and it means that it will work
>> only for NVMe devices that have 1 namespace and will not work for NVMf
>> drivers.
> I am aware shared tags don't get to use the batched queueing, but that's
> orthogonal to this series.

Yes. This series probably should be squashed to Jens's and merged together.

> Most PCIe NVMe SSDs only have 1 namespace, so it generally works out for
> those.

There are SSDs that support NS management and also devices that support 
multiple NS (NVIDIA's NVMe SNAP device support many NSs).

Also all the fabrics controllers support it.

I don't think we need to restrict capable controllers from not working 
with the batching feature from day 1.

>
>> Unless, we'll do some changes in the block layer and/or remove this
>> condition.
> I think it just may work if we export blk_mq_get_driver_tag().

do you have a suggestion for the NVMe/PCI driver ?

I can run it in my lab if you don't have an SSD with more than 1 NS..