linux-kernel - Re: PREEMPT

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Message-ID: <20130807211237.GM6104@pengutronix.de>
Date:	Wed, 7 Aug 2013 23:12:37 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: PREEMPT_RT vs bcache

On Wed, Aug 07, 2013 at 01:53:57PM -0700, Kent Overstreet wrote:
> On Wed, Aug 07, 2013 at 10:28:18PM +0200, Ben Hutchings wrote:
> > As Kent said back in 2011 (commit 84759c6d18c5), bcache needs
> > {down,up}_read_non_owner().  But these are not implemented by the -rt
> > patchset when PREEMPT_RT_FULL is enabled.  Can they be added, or is
> > there a fundamental conflict here?
> 
> You should be able to cherry pick
> 84759c6d18c5144432781ddca037d929ee9db8a5 (Revert "rw_semaphore: remove
> up/down_read_non_owner") - that went in when bcache was merged.
That doesn't help with PREEMPT_RT_FULL because include/linux/rwsem.h
looks like:

	[ ... some includes ... ]
	#ifdef CONFIG_PREEMPT_RT_FULL
	#include <linux/rwsem_rt.h>
	#else /* PREEMPT_RT_FULL */
	[ ... vanilla content including definitions of {down,up}_read_non_owner]
	#endif

So Ben's question was how (if at all) we should implement
{down,up}_read_non_owner for PREEMPT_RT_FULL.
Is it save to just use the vanilla implementation on RT?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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