linux-kernel - Re: [PATCH v2 2/2] locktorture: Make the rt

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Date:   Fri, 9 Dec 2022 21:51:10 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        connoro@...gle.com
Subject: Re: [PATCH v2 2/2] locktorture: Make the rt_boost factor a tunable

On Fri, Dec 9, 2022 at 5:02 PM Davidlohr Bueso <dave@...olabs.net> wrote:
>
> On Fri, 09 Dec 2022, Joel Fernandes (Google) wrote:
>
> >The rt boosting in locktorture has a factor variable s currently large enough
> >that boosting only happens once every minute or so. Add a tunable to reduce the
> >factor so that boosting happens more often, to test paths and arrive at failure
> >modes earlier. With this change, I can set the factor to like 50 and have the
> >boosting happens every 10 seconds or so.
> >
> >Tested with boot parameters:
> >locktorture.torture_type=mutex_lock
> >locktorture.onoff_interval=1
> >locktorture.nwriters_stress=8
> >locktorture.stutter=0
> >locktorture.rt_boost=1
> >locktorture.rt_boost_factor=50
> >locktorture.nlocks=3
> >
> >Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
>
> Reviewed-by: Davidlohr Bueso <dave@...olabs.net>

Thank you!

> >---
> > kernel/locking/locktorture.c | 12 +++++++-----
> > 1 file changed, 7 insertions(+), 5 deletions(-)
> >
> >diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> >index 8968fd65a90d..b64a528e511c 100644
> >--- a/kernel/locking/locktorture.c
> >+++ b/kernel/locking/locktorture.c
> >@@ -48,6 +48,7 @@ torture_param(int, stat_interval, 60,
> > torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
> > torture_param(int, rt_boost, 2,
> >               "Do periodic rt-boost. 0=Disable, 1=Only for rt_mutex, 2=For all lock types.");
> >+torture_param(int, rt_boost_factor, 50, "A factor determining how often rt-boost happens.");
> > torture_param(int, verbose, 1,
> >            "Enable verbose debugging printk()s");
> > torture_param(int, nlocks, 1,
> >@@ -133,12 +134,12 @@ static void torture_lock_busted_write_unlock(int tid __maybe_unused)
> >
> > static void __torture_rt_boost(struct torture_random_state *trsp)
> > {
> >-      const unsigned int factor = 50000; /* yes, quite arbitrary */
> >+      const unsigned int factor = rt_boost_factor;
> >
> >       if (!rt_task(current)) {
> >               /*
> >-               * Boost priority once every ~50k operations. When the
> >-               * task tries to take the lock, the rtmutex it will account
> >+               * Boost priority once every rt_boost_factor operations. When
> >+               * the task tries to take the lock, the rtmutex it will account
>
> Nit: maybe refer to it as 'rt_boost_factor'?

Sorry, I did not follow. Refer to what?

thanks,

 - Joel


>
> >                * for the new priority, and do any corresponding pi-dance.
> >                */
> >               if (trsp && !(torture_random(trsp) %
> >@@ -148,8 +149,9 @@ static void __torture_rt_boost(struct torture_random_state *trsp)
> >                       return;
> >       } else {
> >               /*
> >-               * The task will remain boosted for another ~500k operations,
> >-               * then restored back to its original prio, and so forth.
> >+               * The task will remain boosted for another 10*rt_boost_factor
> >+               * operations, then restored back to its original prio, and so
> >+               * forth.
> >                *
> >                * When @trsp is nil, we want to force-reset the task for
> >                * stopping the kthread.
> >--
> >2.39.0.rc1.256.g54fd8350bd-goog
> >