Re: [PATCHSET 0/4] Add support for shared io-wq backends

[Jens Axboe <axboe@kernel.dk>]

On 1/24/20 2:51 AM, Stefan Metzmacher wrote:
> Hi Jens,
> 
>> Sometimes an applications wants to use multiple smaller rings, because
>> it's more efficient than sharing a ring. The downside of that is that
>> we'll create the io-wq backend separately for all of them, while they
>> would be perfectly happy just sharing that.
>>
>> This patchset adds support for that. io_uring_params grows an 'id' field,
>> which denotes an identifier for the async backend. If an application
>> wants to utilize sharing, it'll simply grab the id from the first ring
>> created, and pass it in to the next one and set IORING_SETUP_SHARED. This
>> allows efficient sharing of backend resources, while allowing multiple
>> rings in the application or library.
> 
> But still all rings need to use the same creds, correct?

Right

>> Not a huge fan of the IORING_SETUP_SHARED name, we should probably make
>> that better (I'm taking suggestions).
> 
> The flag is supposed to be used for the new ring that attached to
> the existing workqueue, correct?

Yes - any ring setup will return an id in the io_uring_params, attaching
to an existing one is done by setting the flag and putting the id number
you want to attach to in there.

> What about IORING_ATTACH_TO_WORKQUEUE?

Trying to avoid something that is too tied to the internals, but workqueue
(or wq) is probably generic enough that it can be used.
IORING_SETUP_ATTACH_WQ?

-- 
Jens Axboe