On Wed, 28 Feb 2018 17:21:44 -0800
"Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> > Perhaps, still think this is a special case. That said, perhaps
> > cond_resched isn't done in critical locations as it's a place that is
> > explicitly stating that it's OK to schedule.
>
> Building on your second sentence, when you are running a non-production
> stress test, adding an extra function call and conditional branch to
> cond_resched() should not be a problem.
>
> So how about the (still untested) patch below?
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit e9a6ea9fc2542459f9a63cf2b3a0264d09fbc266
> Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Date: Sun Feb 25 10:40:44 2018 -0800
>
> EXP sched: Make non-production PREEMPT cond_resched() help Tasks RCU
>
> In CONFIG_PREEMPT=y kernels, cond_resched() is a complete no-op, and
> thus cannot help advance Tasks-RCU grace periods. However, such grace
> periods are only an issue in non-production benchmarking runs of the
> Linux kernel. This commit therefore makes cond_resched() invoke
> rcu_note_voluntary_context_switch() for kernels implementing Tasks RCU
> even in CONFIG_PREEMPT=y kernels.
>
> Reported-by: Steven Rostedt <rost...@goodmis.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b161ef8a902e..970dadefb86f 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1589,6 +1589,12 @@ static inline int test_tsk_need_resched(struct
> task_struct *tsk)
> */
> #ifndef CONFIG_PREEMPT
> extern int _cond_resched(void);
> +#elif defined(CONFIG_TRACEPOINT_BENCHMARK)
> +static inline int _cond_resched(void)
> +{
> + rcu_note_voluntary_context_switch(current);
The thing I hate about this is that it is invasive to code outside of
the tracepoint benchmark. Why do the rcu_note_voluntary_context_switch
here and not in the tracepoint code? Seems odd to have it called
everywhere in the kernel when it is only needed by the benchmark
tracepoint code.
-- Steve
> + return 0;
> +}
> #else
> static inline int _cond_resched(void) { return 0; }
> #endif
