linux-kernel - Re: [PATCH] tracing: Have the trace_event benchmark thread call cond_resched_rcu

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Date:   Tue, 11 Apr 2017 16:47:20 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Have the trace_event benchmark thread call
 cond_resched_rcu_qs()

On Tue, Apr 11, 2017 at 06:56:01PM -0400, Steven Rostedt wrote:
> On Tue, 11 Apr 2017 18:54:35 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> > 
> > The trace_event benchmark thread runs in kernel space in an infinite loop
> > while also calling cond_resched() in case anything else wants to schedule
> > in. Unfortunately, on a PREEMPT kernel, that makes it a nop, in which case,
> > this will never voluntarily schedule. That will cause synchronize_rcu_tasks()
> > to forever block on this thread, while it is running.
> > 
> > This is exactly what cond_resched_rcu_qs() is for. Use that instead.
> > 
> > Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> This actually should be:
> 
> Recommended-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

And:

Acked-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

> -- Steve
> 
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > ---
>