linux-kernel - Re: [PATCH] Make rcutorture more vicious: reinstate boot-time testing

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Date:	Wed, 18 Jun 2008 17:42:29 -0700
From:	Josh Triplett <josh@...edesktop.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, dvhltc@...ibm.com,
	niv@...ibm.com, dino@...ibm.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, vegard.nossum@...il.com,
	adobriyan@...il.com, oleg@...sign.ru, bunk@...nel.org, rjw@...k.pl
Subject: Re: [PATCH] Make rcutorture more vicious: reinstate boot-time testing

Paul E. McKenney wrote:
> Hello again!
> 
> This patch re-institutes the ability to build rcutorture directly into
> the Linux kernel.  The reason that this capability was removed was that
> this could result in your kernel being pretty much useless, as rcutorture
> would be running starting from early boot.  This problem has been avoided
> by (1) making rcutorture run only three seconds of every six by default,
> (2) adding a CONFIG_RCU_TORTURE_TEST_RUNNABLE that permits rcutorture
> to be quiesced at boot time, and (3) adding a sysctl in /proc named
> /proc/sys/kernel/rcutorture_runnable that permits rcutorture to be
> quiesced and unquiesced when built into the kernel.
> 
> Please note that this /proc file is -not- available when rcutorture
> is built as a module.  Please also note that to get the earlier
> take-no-prisoners behavior, you must use the boot command line to set
> rcutorture's "stutter" parameter to zero.
> 
> The rcutorture quiescing mechanism is currently quite crude: loops
> in each rcutorture process that poll a global variable once per tick.
> Suggestions for improvement are welcome.  The default action will
> be to reduce the polling rate to a few times per second.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Suggested-by: Ingo Molnar <mingo@...e.hu>

This patch looks quite reasonable to me.

Signed-off-by: Josh Triplett <josh@...nel.org>

- Josh Triplett

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