Re: [PATCH 00/13] ibmvfc: initial MQ development

[Hannes Reinecke]

On 11/26/20 2:48 AM, Tyrel Datwyler wrote:
> Recent updates in pHyp Firmware and VIOS releases provide new infrastructure
> towards enabling Subordinate Command Response Queues (Sub-CRQs) such that each
> Sub-CRQ is a channel backed by an actual hardware queue in the FC stack on the
> partner VIOS. Sub-CRQs are registered with the firmware via hypercalls and then
> negotiated with the VIOS via new Management Datagrams (MADs) for channel setup.
>
> This initial implementation adds the necessary Sub-CRQ framework and implements
> the new MADs for negotiating and assigning a set of Sub-CRQs to associated VIOS
> HW backed channels. The event pool and locking still leverages the legacy single
> queue implementation, and as such lock contention is problematic when increasing
> the number of queues. However, this initial work demonstrates a 1.2x factor
> increase in IOPs when configured with two HW queues despite lock contention.
Why do you still hold the hold lock during submission?
An initial check on the submission code path didn't reveal anything 
obvious, so it _should_ be possible to drop the host lock there.
Or at least move it into the submission function itself to avoid lock 
contention. Hmm?

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
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