RCU Archive on lore.kernel.org
 help / color / Atom feed
From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 5/6] rcu/trace: Add tracing for how segcb list changes
Date: Tue,  5 Jan 2021 17:26:16 -0800
Message-ID: <20210106012617.14122-5-paulmck@kernel.org> (raw)
In-Reply-To: <20210106012541.GA13972@paulmck-ThinkPad-P72>

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

This commit adds tracing to track how the segcb list changes before/after
acceleration, during queuing and during dequeuing.

This tracing helped discover an optimization that avoided needless GP
requests when no callbacks were accelerated. The tracing overhead is
minimal as each segment's length is now stored in the respective segment.

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/trace/events/rcu.h | 26 ++++++++++++++++++++++++++
 kernel/rcu/tree.c          |  9 +++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 155b5cb..5fc2940 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -505,6 +505,32 @@ TRACE_EVENT_RCU(rcu_callback,
 		  __entry->qlen)
 );
 
+TRACE_EVENT_RCU(rcu_segcb_stats,
+
+		TP_PROTO(struct rcu_segcblist *rs, const char *ctx),
+
+		TP_ARGS(rs, ctx),
+
+		TP_STRUCT__entry(
+			__field(const char *, ctx)
+			__array(unsigned long, gp_seq, RCU_CBLIST_NSEGS)
+			__array(long, seglen, RCU_CBLIST_NSEGS)
+		),
+
+		TP_fast_assign(
+			__entry->ctx = ctx;
+			memcpy(__entry->seglen, rs->seglen, RCU_CBLIST_NSEGS * sizeof(long));
+			memcpy(__entry->gp_seq, rs->gp_seq, RCU_CBLIST_NSEGS * sizeof(unsigned long));
+
+		),
+
+		TP_printk("%s seglen: (DONE=%ld, WAIT=%ld, NEXT_READY=%ld, NEXT=%ld) "
+			  "gp_seq: (DONE=%lu, WAIT=%lu, NEXT_READY=%lu, NEXT=%lu)", __entry->ctx,
+			  __entry->seglen[0], __entry->seglen[1], __entry->seglen[2], __entry->seglen[3],
+			  __entry->gp_seq[0], __entry->gp_seq[1], __entry->gp_seq[2], __entry->gp_seq[3])
+
+);
+
 /*
  * Tracepoint for the registration of a single RCU callback of the special
  * kvfree() form.  The first argument is the RCU type, the second argument
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b0fb654..6bf269c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1495,6 +1495,8 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
 	if (!rcu_segcblist_pend_cbs(&rdp->cblist))
 		return false;
 
+	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
+
 	/*
 	 * Callbacks are often registered with incomplete grace-period
 	 * information.  Something about the fact that getting exact
@@ -1515,6 +1517,8 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
 	else
 		trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
 
+	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
+
 	return ret;
 }
 
@@ -2471,11 +2475,14 @@ static void rcu_do_batch(struct rcu_data *rdp)
 	rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
 	if (offloaded)
 		rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
+
+	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
 	rcu_nocb_unlock_irqrestore(rdp, flags);
 
 	/* Invoke callbacks. */
 	tick_dep_set_task(current, TICK_DEP_BIT_RCU);
 	rhp = rcu_cblist_dequeue(&rcl);
+
 	for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
 		rcu_callback_t f;
 
@@ -2987,6 +2994,8 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
 		trace_rcu_callback(rcu_state.name, head,
 				   rcu_segcblist_n_cbs(&rdp->cblist));
 
+	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
+
 	/* Go handle any RCU core processing required. */
 	if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
 		__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
-- 
2.9.5


  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06  1:25 [PATCH tip/core/rcu 0/6] Track callbacks on a per-segment basis Paul E. McKenney
2021-01-06  1:26 ` [PATCH tip/core/rcu 1/6] rcu/tree: Make rcu_do_batch count how many callbacks were executed paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 2/6] rcu/segcblist: Add additional comments to explain smp_mb() paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 3/6] rcu/segcblist: Add counters to segcblist datastructure paulmck
2021-01-06  1:26 ` [PATCH tip/core/rcu 4/6] rcu/tree: segcblist: Remove redundant smp_mb()s paulmck
2021-01-06  1:26 ` paulmck [this message]
2021-01-06  1:26 ` [PATCH tip/core/rcu 6/6] rcu/segcblist: Add debug checks for segment lengths paulmck

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210106012617.14122-5-paulmck@kernel.org \
    --to=paulmck@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=dhowells@redhat.com \
    --cc=edumazet@google.com \
    --cc=fweisbec@gmail.com \
    --cc=jiangshanlai@gmail.com \
    --cc=joel@joelfernandes.org \
    --cc=josh@joshtriplett.org \
    --cc=kernel-team@fb.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mathieu.desnoyers@efficios.com \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rcu@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

RCU Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/rcu/0 rcu/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 rcu rcu/ https://lore.kernel.org/rcu \
		rcu@vger.kernel.org
	public-inbox-index rcu

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.rcu


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git