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

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Message-ID: <OF2377E85C.B05BDE94-ONC125731A.006E64A7-C125731A.00714F9E@de.ibm.com>
Date:	Mon, 16 Jul 2007 22:37:44 +0200
From:	Hoang-Nam Nguyen <HNGUYEN@...ibm.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Christoph Raisch <raisch@...ibm.com>,
	"OF-General" <general@...ts.openfabrics.org>,
	Joachim Fenkes <fenkes@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"LinuxPPC-Dev" <linuxppc-dev@...abs.org>,
	Roland Dreier <rolandd@...co.com>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: [PATCH 01/10] IB/ehca: Support for multiple event queues

Roland Dreier <rdreier@...co.com> wrote on 16.07.2007 18:04:26:
> 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.
No, I've no figures to provide here. The background of this dist_eqs
option is actually to allow us testing across all event queues
without to change the testcases resp consumers to use certain
event queue number. Thus, I should comment it as EXPERIMENTAL?
> 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?
Agree in that device driver should not overwrite consumer's policy
of event queue assigment. Since dist_eqs is disabled as default,
there's no issue, isn't it?
Regarding ib_verbs: perhaps we should provide create/destroy_eq()
and let upper level protocols or consumers dictate the assignment
to cq by passing an event queue pointer to create_cq()...
> 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.
Fair enough. However why don't let us gather experience with this
feature now? Should we remove dist_eqs option for more consistency?
Thanks
Nam

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