linux-kernel - Re: preempt-rt, need old style rwlocks for systemtap

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Message-ID: <20080503171627.GC23961@redhat.com>
Date:	Sat, 3 May 2008 13:16:27 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Clark Williams <williams@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: preempt-rt, need old style rwlocks for systemtap

Hi -

On Sat, May 03, 2008 at 09:34:16AM -0500, Clark Williams wrote:
> [...]
> > It has come to my attention that the preempt-rt patch suite
> > deliberately defeats the potential concurrency intended by systemtap's
> > use of rwlocks to permit concurrent readers [...]

> The reason it "defeats" the concurrent behavior is that it's really
> complicated to have concurrent readers with Priority Inheritance, so
> the initial cut of rtmutexes serialized all lock accesses. [...]

Do you believe priority inheritance to be an essential property of
every use of these primitives, regardless of the nature of the
specifical critical sections being protected?  Is there no way & need
to opt out of the extra machinery?

- FChE
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