Re: [PATCH 19/22] aio: support kernel side submission for aio with SCQRING

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On Fri, Dec 21, 2018 at 12:22:33PM -0700, Jens Axboe wrote:
> If an application sets IOCTX_FLAG_SCQTHREAD, the io_context gets a
> single thread backing. If used with buffered IO, this will limit
> the device queue depth to 1, but it will be async, IOs will simply
> be serialized.
> 
> Or an application can set IOCTX_FLAG_SQWQ, in which case the io_context
> gets a work queue backing. The concurrency level is the mininum of
> twice the available CPUs, or the queue depth specific for the context.
> For this mode, we attempt to do buffered reads inline, in case they are
> cached. So we should only punt to a workqueue, if we would have to block
> to get our data.

I'm really worried about having this code present twice.  Do we have
strong use cases for both?  Can't we emulate IOCTX_FLAG_SCQTHREAD good
enough with a workqueue without concurrency management?



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