Messages in this thread | | | Date | Thu, 1 Mar 2018 00:04:04 -0500 | From | Steven Rostedt <> | 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, 28 Feb 2018 17:21:44 -0800 "Paul E. McKenney" <paulmck@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 <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);
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
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