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To: Joachim Fenkes <fenkes@de.ibm.com>
Cc: "LinuxPPC-Dev" <linuxppc-dev@ozlabs.org>,
       LKML <linux-kernel@vger.kernel.org>,
       "OF-General" <general@lists.openfabrics.org>,
       Roland Dreier <rolandd@cisco.com>,
       "Hoang-Nam Nguyen" <hnguyen@de.ibm.com>,
       Christoph Raisch <raisch@de.ibm.com>,
       Stefan Roscher <stefan.roscher@de.ibm.com>
Subject: Re: [PATCH 01/10] IB/ehca: Support for multiple event queues
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	<200707121746.36763.fenkes@de.ibm.com>
From: Roland Dreier <rdreier@cisco.com>
Date: Mon, 16 Jul 2007 09:04:26 -0700
In-Reply-To: <200707121746.36763.fenkes@de.ibm.com> (Joachim Fenkes's message of "Thu, 12 Jul 2007 17:46:35 +0200")
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 > The eHCA driver can now handle multiple event queues (read: interrupt
 > sources) instead of one. The number of available EQs is selected via the
 > nr_eqs module parameter.

 > CQs are either assigned to the EQs based on the comp_vector index or, if the
 > dist_eqs module parameter is supplied, using a round-robin scheme.

Do you have any data on how well this round-robin assignment works?
It seems not quite right to me for the driver to advertise nr_eqs
completion vectors, but then if round-robin is turned on to ignore the
consumer's decision about which vector to use.

Maybe if round-robin is turned on you should report 0 as the number of
completion vectors?  Or maybe we should allow well-known values for
the completion vector passed to ib_create_cq to allow consumers to
specify a policy (like round robin) instead of a particular vector?
Maybe the whole interface is broken and we should only be exposing
policies to consumers instead of the specific vector?

I think I would rather hold off on multiple EQs for this merge window
and plan on having something really solid and thought-out for 2.6.24.

 - R.