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
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