Messages in this thread | | | Date | Thu, 19 Jun 2008 11:29:14 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] Make rcutorture more vicious: reinstate boot-time testing |
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> 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.
applied to tip/core/rcu - thanks Paul!
FYI, yesterday's rcutorture-stutter feature survived a few hundred random bootup tests in -tip testing already.
a possible area for enhancement would be the following code:
static void rcu_stutter_wait(void) { while (stutter_pause_test || !rcutorture_runnable) schedule_timeout_interruptible(1); }
will cause HZ number of IRQs on nohz systems, even if rcutorture is disabled. While it's fine to poll if rcutorture_runnable==1, the sleep should be at least 1 second when !rcutorture_runnable.
[ Or it might even make sense to completely stop the threads from a sysctl handler - to make it event-driven and to cause no extra IRQs at all when rcutorture is disabled via /proc. ]
Ingo
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