Messages in this thread | | | Date | Tue, 17 Jul 2018 10:11:21 -0700 | From | Joel Fernandes <> | Subject | Re: [PATCH v10 2/3] tracepoint: Make rcuidle tracepoint callers use SRCU |
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On Sat, Jul 14, 2018 at 10:31:57AM -0400, Mathieu Desnoyers wrote: > ----- On Jul 13, 2018, at 5:55 PM, Joel Fernandes, Google joel@joelfernandes.org wrote: > > > From: "Joel Fernandes (Google)" <joel@joelfernandes.org> > > > > In recent tests with IRQ on/off tracepoints, a large performance > > overhead ~10% is noticed when running hackbench. This is root caused to > > calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the > > tracepoint code. Following a long discussion on the list [1] about this, > > we concluded that srcu is a better alternative for use during rcu idle. > > Although it does involve extra barriers, its lighter than the sched-rcu > > version which has to do additional RCU calls to notify RCU idle about > > entry into RCU sections. > > > > In this patch, we change the underlying implementation of the > > trace_*_rcuidle API to use SRCU. This has shown to improve performance > > alot for the high frequency irq enable/disable tracepoints. > > > > Test: Tested idle and preempt/irq tracepoints. > > > > Here are some performance numbers: > > > > With a run of the following 30 times on a single core x86 Qemu instance > > with 1GB memory: > > hackbench -g 4 -f 2 -l 3000 > > > > Completion times in seconds. CONFIG_PROVE_LOCKING=y. > > > > No patches (without this series) > > Mean: 3.048 > > Median: 3.025 > > Std Dev: 0.064 > > > > With Lockdep using irq tracepoints with RCU implementation: > > Mean: 3.451 (-11.66 %) > > Median: 3.447 (-12.22%) > > Std Dev: 0.049 > > > > With Lockdep using irq tracepoints with SRCU implementation (this series): > > Mean: 3.020 (I would consider the improvement against the "without > > this series" case as just noise). > > Median: 3.013 > > Std Dev: 0.033 > > > > [1] https://patchwork.kernel.org/patch/10344297/ > > > > Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > I'm fine with the changes done since last iteration. > > Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thanks a lot Mathieu!
Steve, Peter, looks good to you too now?
thanks,
- Joel
[...] > > Cleaned-up-by: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > > --- > > include/linux/tracepoint.h | 45 +++++++++++++++++++++++++++++++------- > > kernel/tracepoint.c | 16 +++++++++++++- > > 2 files changed, 52 insertions(+), 9 deletions(-) > > > > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > > index 19a690b559ca..97e1d365a817 100644 > > --- a/include/linux/tracepoint.h > > +++ b/include/linux/tracepoint.h > > @@ -15,6 +15,7 @@ > > */ > > > > #include <linux/smp.h> > > +#include <linux/srcu.h> > > #include <linux/errno.h> > > #include <linux/types.h> > > #include <linux/cpumask.h> > > @@ -33,6 +34,8 @@ struct trace_eval_map { > > > > #define TRACEPOINT_DEFAULT_PRIO 10 > > > > +extern struct srcu_struct tracepoint_srcu; > > + > > extern int > > tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data); > > extern int > > @@ -75,10 +78,16 @@ int unregister_tracepoint_module_notifier(struct > > notifier_block *nb) > > * probe unregistration and the end of module exit to make sure there is no > > * caller executing a probe when it is freed. > > */ > > +#ifdef CONFIG_TRACEPOINTS > > static inline void tracepoint_synchronize_unregister(void) > > { > > + synchronize_srcu(&tracepoint_srcu); > > synchronize_sched(); > > } > > +#else > > +static inline void tracepoint_synchronize_unregister(void) > > +{ } > > +#endif > > > > #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS > > extern int syscall_regfunc(void); > > @@ -129,18 +138,34 @@ extern void syscall_unregfunc(void); > > * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just > > * "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto". > > */ > > -#define __DO_TRACE(tp, proto, args, cond, rcucheck) \ > > +#define __DO_TRACE(tp, proto, args, cond, rcuidle) \ > > do { \ > > struct tracepoint_func *it_func_ptr; \ > > void *it_func; \ > > void *__data; \ > > + int __maybe_unused idx = 0; \ > > \ > > if (!(cond)) \ > > return; \ > > - if (rcucheck) \ > > - rcu_irq_enter_irqson(); \ > > - rcu_read_lock_sched_notrace(); \ > > - it_func_ptr = rcu_dereference_sched((tp)->funcs); \ > > + \ > > + /* srcu can't be used from NMI */ \ > > + if (rcuidle && in_nmi()) \ > > + WARN_ON_ONCE(1); \ > > + \ > > + /* keep srcu and sched-rcu usage consistent */ \ > > + preempt_disable_notrace(); \ > > + \ > > + /* \ > > + * For rcuidle callers, use srcu since sched-rcu \ > > + * doesn't work from the idle path. \ > > + */ \ > > + if (rcuidle) \ > > + idx = srcu_read_lock_notrace(&tracepoint_srcu); \ > > + else \ > > + rcu_read_lock_sched_notrace(); \ > > + \ > > + it_func_ptr = rcu_dereference_raw((tp)->funcs); \ > > + \ > > if (it_func_ptr) { \ > > do { \ > > it_func = (it_func_ptr)->func; \ > > @@ -148,9 +173,13 @@ extern void syscall_unregfunc(void); > > ((void(*)(proto))(it_func))(args); \ > > } while ((++it_func_ptr)->func); \ > > } \ > > - rcu_read_unlock_sched_notrace(); \ > > - if (rcucheck) \ > > - rcu_irq_exit_irqson(); \ > > + \ > > + if (rcuidle) \ > > + srcu_read_unlock_notrace(&tracepoint_srcu, idx);\ > > + else \ > > + rcu_read_unlock_sched_notrace(); \ > > + \ > > + preempt_enable_notrace(); \ > > } while (0) > > > > #ifndef MODULE > > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c > > index 6dc6356c3327..955148d91b74 100644 > > --- a/kernel/tracepoint.c > > +++ b/kernel/tracepoint.c > > @@ -31,6 +31,9 @@ > > extern struct tracepoint * const __start___tracepoints_ptrs[]; > > extern struct tracepoint * const __stop___tracepoints_ptrs[]; > > > > +DEFINE_SRCU(tracepoint_srcu); > > +EXPORT_SYMBOL_GPL(tracepoint_srcu); > > + > > /* Set to 1 to enable tracepoint debug output */ > > static const int tracepoint_debug; > > > > @@ -67,16 +70,27 @@ static inline void *allocate_probes(int count) > > return p == NULL ? NULL : p->probes; > > } > > > > -static void rcu_free_old_probes(struct rcu_head *head) > > +static void srcu_free_old_probes(struct rcu_head *head) > > { > > kfree(container_of(head, struct tp_probes, rcu)); > > } > > > > +static void rcu_free_old_probes(struct rcu_head *head) > > +{ > > + call_srcu(&tracepoint_srcu, head, srcu_free_old_probes); > > +} > > + > > static inline void release_probes(struct tracepoint_func *old) > > { > > if (old) { > > struct tp_probes *tp_probes = container_of(old, > > struct tp_probes, probes[0]); > > + /* > > + * Tracepoint probes are protected by both sched RCU and SRCU, > > + * by calling the SRCU callback in the sched RCU callback we > > + * cover both cases. So let us chain the SRCU and sched RCU > > + * callbacks to wait for both grace periods. > > + */ > > call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes); > > } > > } > > -- > > 2.18.0.203.gfac676dfb9-goog > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com
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