Re: [PATCH 2/9] IB: add a proper completion queue abstraction

From: Bart Van Assche
Date: Sun Nov 22 2015 - 11:57:12 EST

On 11/22/15 06:57, Sagi Grimberg wrote:
I think that bart wants to allow the caller to select cpu affinity
per CQ. In this case ib_alloc_cq in workqueue mode would need to
accept a affinity_hint from the caller (default to wild-card

Hmm, true. How would be set that hint from userspace? I'd really prefer
to see a practical justification for it first.

In order to assign CPUs from user-space we'd need an ethtool like
interface for isert/srpt/<xxxt>. Given that this is something we don't
want to get into right now, I assumed that Bart meant that srpt
would take a "least used" approach from srpt driver (which isn't better
taking the wild-card option I'd say), So I'll let Bart answer...

Hello Christoph and Sagi,

My intention is indeed to allow to control CPU affinity per CQ. One use case is to implement a least-used policy in RDMA drivers that use multiple completion queues. Another use case is to make CPU affinity configurable from user space through something similar to ethtool or via sysfs.

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