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, dipankar@in.ibm.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,
sfr@canb.auug.org.au, "Paul E. McKenney" <paulmck@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Jiri Olsa <jolsa@redhat.com>,
bpf@vger.kernel.org
Subject: [PATCH tip/core/rcu 3/8] rcu-tasks: Use more aggressive polling for RCU Tasks Trace
Date: Thu, 17 Sep 2020 14:07:39 -0700 [thread overview]
Message-ID: <20200917210744.2995-3-paulmck@kernel.org> (raw)
In-Reply-To: <20200917210652.GA31242@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
The RCU Tasks Trace grace periods are too slow, as in 40x slower than
those of RCU Tasks. This is due to my having assumed a one-second grace
period was OK, and thus not having optimized any further. This commit
provides the first step in this optimization process, namely by allowing
the task_list scan backoff interval to be specified on a per-flavor basis,
and then speeding up the scans for RCU Tasks Trace. However, kernels
built with CONFIG_TASKS_TRACE_RCU_READ_MB=y continue to use the old slower
backoff, consistent with that Kconfig option's goal of reducing IPIs.
Link: https://lore.kernel.org/bpf/CAADnVQK_AiX+S_L_A4CQWT11XyveppBbQSQgH_qWGyzu_E8Yeg@mail.gmail.com/
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tasks.h | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 978508e..ad8c4f3 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -28,6 +28,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
* @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
* @gp_func: This flavor's grace-period-wait function.
* @gp_state: Grace period's most recent state transition (debugging).
+ * @init_fract: Initial backoff sleep interval.
* @gp_jiffies: Time of last @gp_state transition.
* @gp_start: Most recent grace-period start in jiffies.
* @n_gps: Number of grace periods completed since boot.
@@ -48,6 +49,7 @@ struct rcu_tasks {
struct wait_queue_head cbs_wq;
raw_spinlock_t cbs_lock;
int gp_state;
+ int init_fract;
unsigned long gp_jiffies;
unsigned long gp_start;
unsigned long n_gps;
@@ -329,8 +331,10 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
*/
lastreport = jiffies;
- /* Start off with HZ/10 wait and slowly back off to 1 HZ wait. */
- fract = 10;
+ // Start off with initial wait and slowly back off to 1 HZ wait.
+ fract = rtp->init_fract;
+ if (fract > HZ)
+ fract = HZ;
for (;;) {
bool firstreport;
@@ -553,6 +557,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
static int __init rcu_spawn_tasks_kthread(void)
{
+ rcu_tasks.init_fract = 10;
rcu_tasks.pregp_func = rcu_tasks_pregp_step;
rcu_tasks.pertask_func = rcu_tasks_pertask;
rcu_tasks.postscan_func = rcu_tasks_postscan;
@@ -1163,6 +1168,13 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace);
static int __init rcu_spawn_tasks_trace_kthread(void)
{
+ if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) {
+ rcu_tasks_trace.init_fract = 10;
+ } else {
+ rcu_tasks_trace.init_fract = HZ / 5;
+ if (rcu_tasks_trace.init_fract <= 0)
+ rcu_tasks_trace.init_fract = 1;
+ }
rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step;
rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask;
rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan;
--
2.9.5
next prev parent reply other threads:[~2020-09-17 21:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 20:19 [PATCH RFC tip/core/rcu 0/4] Accelerate RCU Tasks Trace updates Paul E. McKenney
2020-09-10 20:20 ` [PATCH RFC tip/core/rcu 1/4] rcu-tasks: Mark variables static paulmck
2020-09-10 20:20 ` [PATCH RFC tip/core/rcu 2/4] rcu-tasks: Use more aggressive polling for RCU Tasks Trace paulmck
2020-09-10 20:20 ` [PATCH RFC tip/core/rcu 3/4] rcu-tasks: Selectively enable more RCU Tasks Trace IPIs paulmck
2020-09-10 20:20 ` [PATCH RFC tip/core/rcu 4/4] rcu-tasks: Shorten per-grace-period sleep for RCU Tasks Trace paulmck
2020-09-11 3:18 ` Alexei Starovoitov
2020-09-11 4:37 ` Paul E. McKenney
2020-09-17 21:06 ` [PATCH RFC tip/core/rcu 0/4] Accelerate RCU Tasks Trace updates Paul E. McKenney
2020-09-17 21:07 ` [PATCH tip/core/rcu 1/8] rcu-tasks: Prevent complaints of unused show_rcu_tasks_classic_gp_kthread() paulmck
2020-09-17 21:07 ` [PATCH tip/core/rcu 2/8] rcu-tasks: Mark variables static paulmck
2020-09-17 21:07 ` paulmck [this message]
2020-09-17 21:07 ` [PATCH tip/core/rcu 4/8] rcu-tasks: Selectively enable more RCU Tasks Trace IPIs paulmck
2020-09-17 21:07 ` [PATCH tip/core/rcu 5/8] rcu-tasks: Shorten per-grace-period sleep for RCU Tasks Trace paulmck
2020-09-17 21:07 ` [PATCH tip/core/rcu 6/8] rcu-tasks: Fix grace-period/unlock race in " paulmck
2020-09-17 21:07 ` [PATCH tip/core/rcu 7/8] rcu-tasks: Fix low-probability task_struct leak paulmck
2020-09-17 21:07 ` [PATCH tip/core/rcu 8/8] rcu-tasks: Enclose task-list scan in rcu_read_lock() 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=20200917210744.2995-3-paulmck@kernel.org \
--to=paulmck@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=dhowells@redhat.com \
--cc=dipankar@in.ibm.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=jolsa@redhat.com \
--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=sfr@canb.auug.org.au \
--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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).