On 06/19/2017 08:31 AM, Jens Axboe wrote:
> On 06/19/2017 12:25 AM, Christoph Hellwig wrote:
>> On Sat, Jun 17, 2017 at 09:11:30AM -0600, Jens Axboe wrote:
>>> I have two samples here, and I just tested, and both of them want it
>>> assigned with nsid=0xffffffff or they will fail the writes... So I'd say
>>> we're better off ensuring we do allocate them globally.
>>
>> That's clearly against the spec. I'd say go to your vendor and get
>> a refund, as we Linux folks (Martin and I) fought for this so that
>> we would not have to do the explicit allocations.
>>
>> Another quote for from the spec:
>>
>> "Streams are opened by the controller when the host issues a write
>> command that specifies a stream identifier that is not currently open.
>> While a stream is open the controller maintains context for that stream
>> (e.g., buffers for associated data). The host may determine the streams
>> that are open using the Get Status operation."
>>
>> And I think this is very important - otherwise you need to either
>> allocate the stremas beforehand as your earlier patches (and we take
>> away the resources from the 99% of the users not using write life
>> hints), or we need the lazy allocation scheme. And for that to be
>> efficient it probably needs to be lazy per-stream allocation. That's
>> why we got the implicit open in after all.
>
> These are just samples, so no refund possible! As you might remember,
> I was pretty adamant on not wanting explicit open/close as well, back
> in those days. I'll check with the vendor and see what's going on.
Looking at it a bit more closely - there's a difference between
assigning X number of streams (allocating) for use by the subsystem or
per-ns, and having to manually open them. So I don't necessarily think
there's a problem here, neither for us or on the device.
If I load the driver as it currently stands, and get streams params
after load:
Number of Open Streams in NVM subsystem (NOSNS): 0
Allocated Stream Resources (ASR): 4
Number of Open Streams in Namespace (NOSN): 0
4 streams allocated, 0 currently open. Then I generate a single write to
some stream ID:
Number of Open Streams in NVM subsystem (NOSNS): 1
Allocated Stream Resources (ASR): 4
Number of Open Streams in Namespace (NOSN): 1
and we know see a single stream actually open, implicitly, by the
device. Fire off another single stream write, this time to another
stream, and we get:
Number of Open Streams in NVM subsystem (NOSNS): 2
Allocated Stream Resources (ASR): 4
Number of Open Streams in Namespace (NOSN): 2
and stream status correctly reflects that I did a WRITE_HINT_SHORT and
WRITE_HINT_LONG write:
Open Stream Count : 2
Stream Identifier 000001 : 1
Stream Identifier 000002 : 3
Awaiting clarification from the vendor what their position/view of this
is. Reading the spec, I do agree that it leans towards only needing
allocation for a specific name space, but it doesn't explicitly say that
you can use any of the available streams, without allocation, if they
haven't been assigned to a specific name space. I would interpret it
that way, though.
--
Jens Axboe
