Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements

From: Jens Axboe
Date: Fri Sep 09 2016 - 19:37:42 EST

On 09/09/2016 05:00 PM, Josef Bacik wrote:
Right. Alternatively, you could perhaps make it so that the lost
connection is removed, unack'd requests on that connection are resent,
and the session moves on with one less connection (unless the lost
connection is the last one, in which case we die as before). That might
be too much work and not worth it though.

Yeah I wasn't sure if we could just randomly remove hw queue's in blk mq
while the device is still up. If that is in fact easy to do then I'm in
favor of trucking along with less connections than we originally had,
otherwise I think it'll be too big of a pain. Also some users (Facebook
in this case) would rather the whole thing fail so we can figure out
what went wrong rather than suddenly going at a degraded performance.

We can do that online. We do that for CPU hotplug/unplug events, and we
also expose that functionality to drivers through
blk_mq_update_nr_hw_queues(). So yes, should be trivial to support from

Jens Axboe