linux-kernel - Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit

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Message-ID: <20200623210111.GA117936@google.com>
Date:   Tue, 23 Jun 2020 17:01:11 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, jiangshanlai@...il.com,
        dipankar@...ibm.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, linux-mm@...ck.org
Subject: Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for
 exit_mmap() CPU stalls

On Tue, Jun 23, 2020 at 01:55:08PM -0700, Paul E. McKenney wrote:
[..] 
> > Just for my understanding, cond_resched_tasks_rcu_qs() may not help here
> > because preemption is not disabled right? Still I see no harm in using it
> > here either as it may give a slight speed up for tasks-RCU.
> 
> The RCU-tasks stall-warning interval is ten minutes, and I have not yet
> seen evidence that we are getting close to that.  If we do, then yes,
> a cond_resched_tasks_rcu_qs() might be in this code's future.  But it
> does add overhead, so we need to see the evidence first.

Yes, true about that overhead. Ok, this is fine with me too, thanks :)

 - Joel