linux-kernel - Question on __torture_rt

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Message-ID: <1393d18f-4928-45da-b504-7e5b6a681e51@paulmck-laptop>
Date:   Mon, 21 Aug 2023 20:12:50 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     joel@...lfernandes.org
Cc:     linux-kernel@...r.kernel.org
Subject: Question on __torture_rt_boost() else clause

Hello, Joel!

A quick question for you...

I am doing catch-up additions of locktorture module parameters
to kernel-parameters.txt, and came across rt_boost_factor.  The
multiplication by cxt.nrealwriters_stress in the !rt_task(current)
then-clause makes sense:  No matter how many writers you have, the
number of boost operations per unit time remains roughly constant.
But I am having some difficulty rationalizing a similar multiplication
in the else-clause.  That would seem to leave boosting in effect for
longer times the more writers there were.

Is that the intent?

Also, I am rationalizing the choice of 2 as default for rt_boost by
noting that "mutex" and "ww_mutex_lock" don't do boosting and that
preemption-disabling makes non-RT spinlocks immune from priority
inversion.  Is this what you had in mind, or am I off in the weeds here?

I am putting my best guess in the patch, and am including you on CC.

						Thanx, Paul