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

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Message-ID: <20170411185601.01b32a0e@gandalf.local.home>
Date:   Tue, 11 Apr 2017 18:56:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Have the trace_event benchmark thread call
 cond_resched_rcu_qs()

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>

-- Steve

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