Re: [Nbd] [PATCH][V3] nbd: add multi-connection support

[Josef Bacik]

On 09/29/2016 12:41 PM, Wouter Verhelst wrote:
> On Thu, Sep 29, 2016 at 10:03:50AM -0400, Josef Bacik wrote:
> > So think of it like normal disks with multiple channels.  We don't send flushes
> > down all the hwq's to make sure they are clear, we leave that decision up to the
> > application (usually a FS of course).
>
> Well, when I asked earlier, Christoph said[1] that blk-mq assumes that
> when a FLUSH is sent over one channel, and the reply comes in, that all
> commands which have been received, regardless of which channel they were
> received over, have reched disk.
>
> [1] Message-ID: <20160915122304.GA15501@xxxxxxxxxxxxx>
>
> It is impossible for nbd to make such a guarantee, due to head-of-line
> blocking on TCP.

Huh I missed that.  Yeah that's not possible for us for sure, I think my option 
idea is the less awful way forward if we want to address that limitation.  Thanks,

Josef