Messages in this thread Patch in this message | | | Date | Wed, 28 Feb 2018 17:21:44 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 06/10] trace: Eliminate cond_resched_rcu_qs() in favor of cond_resched() |
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On Wed, Feb 28, 2018 at 06:12:52PM -0500, Steven Rostedt wrote: > On Tue, 27 Feb 2018 07:36:46 -0800 > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > > > > > --- 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_TASKS_RCU) > > > > +static inline int _cond_resched(void) > > > > +{ > > > > + rcu_note_voluntary_context_switch(current); > > > > + return 0; > > > > +} > > > > #else > > > > static inline int _cond_resched(void) { return 0; } > > > > #endif > > > > > > > > > This does work, but so does the below, without causing cond_resched() > > > from being something other than a nop of CONFIG_PREEMPT. > > > > True, but based on the cond_resched_rcu_qs() experience, I bet that > > trace_benchmark.c won't be the only place needing help. > > 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
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commit e9a6ea9fc2542459f9a63cf2b3a0264d09fbc266 Author: Paul E. McKenney <paulmck@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 <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@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); + return 0; +} #else static inline int _cond_resched(void) { return 0; } #endif
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