linux-kernel - Re: [PATCH 01/10] IB/ehca: Support for multiple event queues

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Message-ID: <adalkdgz65x.fsf@cisco.com>
Date:	Mon, 16 Jul 2007 09:04:26 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Joachim Fenkes <fenkes@...ibm.com>
Cc:	"LinuxPPC-Dev" <linuxppc-dev@...abs.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"OF-General" <general@...ts.openfabrics.org>,
	Roland Dreier <rolandd@...co.com>,
	"Hoang-Nam Nguyen" <hnguyen@...ibm.com>,
	Christoph Raisch <raisch@...ibm.com>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: [PATCH 01/10] IB/ehca: Support for multiple event queues

 > 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.
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