linux-kernel - Re: [PATCH] IB/ehca: Serialize HCA-related hCalls on POWER5

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Date:	Thu, 06 Dec 2007 10:27:09 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linuxppc-dev@...abs.org, Joachim Fenkes <fenkes@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"OF-General" <general@...ts.openfabrics.org>,
	Roland Dreier <rolandd@...co.com>,
	"OF-EWG" <ewg@...ts.openfabrics.org>,
	Stefan Roscher <stefan.roscher@...ibm.com>,
	Christoph Raisch <raisch@...ibm.com>,
	Marcus Eder <meder@...ibm.com>
Subject: Re: [PATCH] IB/ehca: Serialize HCA-related hCalls on POWER5

 > > +               ehca_lock_hcalls = !(cur_cpu_spec->cpu_user_features
 > > +                                    & PPC_FEATURE_ARCH_2_05);

 > We already talked about this yesterday, but I still feel that checking the
 > instruction set of the CPU should not be used to determine whether a
 > specific device driver implementation is used int hypervisor.

I had the same reaction... is testing cpu_user_features really the
best way to detect this issue?

I'll hold off applying this for a few days so you guys can decide the
best thing to do.  We'll definitely get some fix into 2.6.24 but we
have time to make a good decision.

 > Regarding the performance problem, have you checked whether converting all
 > your spin_lock_irqsave to spin_lock/spin_lock_irq improves your performance
 > on the older machines? Maybe it's already fast enough that way.

It does seem that the only places that the hcall_lock is taken also
use msleep, so they must always be in process context.  So you can
safely just use spin_lock(), right?

 - R.
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