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

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Message-ID: <OF82B8C559.721FE4D8-ONC125731A.00700205-C125731A.00711653@de.ibm.com>
Date:	Mon, 16 Jul 2007 22:34:19 +0200
From:	Joachim Fenkes <FENKES@...ibm.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Christoph Raisch <raisch@...ibm.com>,
	"OF-General" <general@...ts.openfabrics.org>,
	Hoang-Nam Nguyen <hnguyen@...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:

> 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.

The round-robin feature was primarily meant as a debug/evaluation feature; 
it is not supposed to be active by default. ULP programmers can, for 
example, quickly evaluate the performance increase that comp_vectors could 
give them, without changing their code. Without this debug option, the 
comp_vector policy is still up to the ULPs.

> Maybe if round-robin is turned on you should report 0 as the number of
> completion vectors?

That sounds like a reasonable idea -- I'll change that right away.

> Maybe the whole interface is broken and we should only be exposing
> policies to consumers instead of the specific vector?

If so, I think the policies should be handled by the IB core code instead 
of being re-invented by each driver. The IB core would then again pass 
actual comp_vector values to the driver.

> 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.

It's your call, but the code is there and I don't expect it to change a 
lot later, so it could be used by others to get a first impression of 
what's possible using comp_vectors and to gather some experience with 
them.

Regards,
  Joachim
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