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SubjectRe: [Nbd] [PATCH][V3] nbd: add multi-connection support
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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@infradead.org>
>
> 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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