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

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Date:	Fri, 7 Dec 2007 10:58:37 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linuxppc-dev@...abs.org
Cc:	Roland Dreier <rdreier@...co.com>,
	Joachim Fenkes <fenkes@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	OF-EWG <ewg@...ts.openfabrics.org>,
	Christoph Raisch <raisch@...ibm.com>,
	Marcus Eder <meder@...ibm.com>,
	OF-General <general@...ts.openfabrics.org>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: [PATCH] IB/ehca: Serialize HCA-related hCalls on POWER5

On Thursday 06 December 2007, Roland Dreier wrote:
>  > 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?

I think it needs some more inspection. The msleep in there is only called
for hcalls that return H_IS_LONG_BUSY(). In theory, you can call
ehca_plpar_hcall_norets() from inside an interrupt handler if the
hcall in question never returns long busy.

	Arnd <><
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