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Date: Fri, 15 Jun 2012 16:35:36 -0700
From: Josh Triplett <josh@...htriplett.org>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
dipankar@...ibm.com, akpm@...ux-foundation.org,
mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
fweisbec@...il.com, patches@...aro.org,
"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 10/15] rcu: Add tracing for _rcu_barrier()
On Fri, Jun 15, 2012 at 02:06:05PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
>
> This commit adds event tracing for _rcu_barrier() execution. This
> is defined only if RCU_TRACE=y.
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
> include/trace/events/rcu.h | 45 ++++++++++++++++++++++++++++++++++++++++++++
> kernel/rcutree.c | 29 +++++++++++++++++++++++++++-
> 2 files changed, 73 insertions(+), 1 deletions(-)
>
> diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> index 1480900..cd63f79 100644
> --- a/include/trace/events/rcu.h
> +++ b/include/trace/events/rcu.h
> @@ -540,6 +540,50 @@ TRACE_EVENT(rcu_torture_read,
> __entry->rcutorturename, __entry->rhp)
> );
>
> +/*
> + * Tracepoint for _rcu_barrier() execution. The string "s" describes
> + * the _rcu_barrier phase:
> + * "Begin": rcu_barrier_callback() started.
> + * "Check": rcu_barrier_callback() checking for piggybacking.
> + * "EarlyExit": rcu_barrier_callback() piggybacked, thus early exit.
> + * "Inc1": rcu_barrier_callback() piggyback check counter incremented.
> + * "Offline": rcu_barrier_callback() found offline CPU
> + * "OnlineQ": rcu_barrier_callback() found online CPU with callbacks.
> + * "OnlineNQ": rcu_barrier_callback() found online CPU, no callbacks.
> + * "IRQ": An rcu_barrier_callback() callback posted on remote CPU.
> + * "CB": An rcu_barrier_callback() invoked a callback, not the last.
> + * "LastCB": An rcu_barrier_callback() invoked the last callback.
> + * "Inc2": rcu_barrier_callback() piggyback check counter incremented.
> + * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
> + * is the count of remaining callbacks, and "done" is the piggybacking count.
> + */
> +TRACE_EVENT(rcu_barrier,
> +
> + TP_PROTO(char *rcuname, char *s, int cpu, int cnt, unsigned long done),
> +
> + TP_ARGS(rcuname, s, cpu, cnt, done),
> +
> + TP_STRUCT__entry(
> + __field(char *, rcuname)
> + __field(char *, s)
> + __field(int, cpu)
> + __field(int, cnt)
> + __field(unsigned long, done)
> + ),
> +
> + TP_fast_assign(
> + __entry->rcuname = rcuname;
> + __entry->s = s;
> + __entry->cpu = cpu;
> + __entry->cnt = cnt;
> + __entry->done = done;
> + ),
> +
> + TP_printk("%s %s cpu %d remaining %d # %lu",
> + __entry->rcuname, __entry->s, __entry->cpu, __entry->cnt,
> + __entry->done)
> +);
> +
> #else /* #ifdef CONFIG_RCU_TRACE */
>
> #define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0)
> @@ -563,6 +607,7 @@ TRACE_EVENT(rcu_torture_read,
> #define trace_rcu_batch_end(rcuname, callbacks_invoked, cb, nr, iit, risk) \
> do { } while (0)
> #define trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
> +#define trace_rcu_barrier(name, s, cpu, cnt, done) do { } while (0)
>
> #endif /* #else #ifdef CONFIG_RCU_TRACE */
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 7c299d3..ebd5223 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -2257,6 +2257,17 @@ static int rcu_cpu_has_callbacks(int cpu)
> }
>
> /*
> + * Helper function for _rcu_barrier() tracing. If tracing is disabled,
> + * the compiler is expected to optimize this away.
> + */
> +static void _rcu_barrier_trace(struct rcu_state *rsp, char *s,
> + int cpu, unsigned long done)
> +{
> + trace_rcu_barrier(rsp->name, s, cpu,
> + atomic_read(&rsp->barrier_cpu_count), done);
> +}
> +
> +/*
> * RCU callback function for _rcu_barrier(). If we are last, wake
> * up the task executing _rcu_barrier().
> */
> @@ -2265,8 +2276,12 @@ static void rcu_barrier_callback(struct rcu_head *rhp)
> struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
> struct rcu_state *rsp = rdp->rsp;
>
> - if (atomic_dec_and_test(&rsp->barrier_cpu_count))
> + if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
> + _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
> complete(&rsp->barrier_completion);
> + } else {
> + _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
> + }
> }
>
> /*
> @@ -2277,6 +2292,7 @@ static void rcu_barrier_func(void *type)
> struct rcu_state *rsp = type;
> struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
>
> + _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
> atomic_inc(&rsp->barrier_cpu_count);
> rsp->call(&rdp->barrier_head, rcu_barrier_callback);
> }
> @@ -2295,6 +2311,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
> unsigned long snap_done;
>
> init_rcu_head_on_stack(&rd.barrier_head);
> + _rcu_barrier_trace(rsp, "Begin", -1, snap);
>
> /* Take mutex to serialize concurrent rcu_barrier() requests. */
> mutex_lock(&rsp->barrier_mutex);
> @@ -2307,7 +2324,9 @@ static void _rcu_barrier(struct rcu_state *rsp)
>
> /* Recheck ->n_barrier_done to see if others did our work for us. */
> snap_done = ACCESS_ONCE(rsp->n_barrier_done);
> + _rcu_barrier_trace(rsp, "Check", -1, snap_done);
> if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
> + _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
> smp_mb();
> mutex_unlock(&rsp->barrier_mutex);
> return;
> @@ -2316,6 +2335,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
> /* Increment ->n_barrier_done to avoid duplicate work. */
> ACCESS_ONCE(rsp->n_barrier_done)++;
> WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
> + _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
> smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
>
> /*
> @@ -2352,13 +2372,19 @@ static void _rcu_barrier(struct rcu_state *rsp)
> preempt_disable();
> rdp = per_cpu_ptr(rsp->rda, cpu);
> if (cpu_is_offline(cpu)) {
> + _rcu_barrier_trace(rsp, "Offline", cpu,
> + rsp->n_barrier_done);
> preempt_enable();
> while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen))
> schedule_timeout_interruptible(1);
> } else if (ACCESS_ONCE(rdp->qlen)) {
> + _rcu_barrier_trace(rsp, "OnlineQ", cpu,
> + rsp->n_barrier_done);
> smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
> preempt_enable();
> } else {
> + _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
> + rsp->n_barrier_done);
> preempt_enable();
> }
> }
> @@ -2391,6 +2417,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
> smp_mb(); /* Keep increment after above mechanism. */
> ACCESS_ONCE(rsp->n_barrier_done)++;
> WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
> + _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
> smp_mb(); /* Keep increment before caller's subsequent code. */
>
> /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
> --
> 1.7.8
>
--
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