Re: [PATCH v2 4/4] nbd: Enable multi-conn using round-robin

["Richard W.M. Jones" <rjones@redhat.com>]

On Mon, Apr 28, 2025 at 01:46:47PM -0500, Eric Blake wrote:
[...]

This all looks similar to when I posted it before.  However I noted a
couple of problems ...

> (XXX) The strategy here is very naive.  Firstly if you were going to 
> open them, you'd probably want to open them in parallel.  Secondly it
> would make sense to delay opening until multiple parallel requests are
> seen (perhaps above some threshold), so that simple or shortlived NBD
> operations do not require multiple connections to be made.

> (XXX) This uses a naive round-robin approach which could be improved.
> For example we could look at how many requests are in flight and
> assign operations to the connections with fewest.  Or we could try to
> estimate (based on size of requests outstanding) the load on each
> connection.  But this implementation doesn't do any of that.

Plus there was a third rather more fundamental problem that apparently
I didn't write about.  That is that connections were serialised on a
single thread (called from many coroutines).  This bottleneck meant
that there wasn't very much advantage to multi-conn, compared to what
we get in libnbd / nbdcopy.

Are these fixed / planned to be fixed, especially the third?

Rich.

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