Some workloads do isolated RCU work, and this can affect operation
latencies. This commit therefore adds a writer_holdoff_jiffies module
parameter that causes writers to block for the specified number of
jiffies between each pair of consecutive write-side operations.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 5 +++++
kernel/rcu/rcuscale.c | 4 ++++
2 files changed, 9 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a1457995fd41..5ba231b786f8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4983,6 +4983,11 @@
in microseconds. The default of zero says
no holdoff.
+ rcuscale.writer_holdoff_jiffies= [KNL]
+ Additional write-side holdoff between grace
+ periods, but in jiffies. The default of zero
+ says no holdoff.
+
rcutorture.fqs_duration= [KNL]
Set duration of force_quiescent_state bursts
in microseconds.
diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index d1221731c7cf..4277037e0996 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -93,6 +93,7 @@ torture_param(bool, shutdown, RCUSCALE_SHUTDOWN,
"Shutdown at end of scalability tests.");
torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");
+torture_param(int, writer_holdoff_jiffies, 0, "Holdoff (jiffies) between GPs, zero to disable");
torture_param(int, kfree_rcu_test, 0, "Do we run a kfree_rcu() scale test?");
torture_param(int, kfree_mult, 1, "Multiple of kfree_obj size to allocate.");
torture_param(int, kfree_by_call_rcu, 0, "Use call_rcu() to emulate kfree_rcu()?");
@@ -414,6 +415,7 @@ rcu_scale_writer(void *arg)
struct rcu_head *rhp = NULL;
bool started = false, done = false, alldone = false;
u64 t;
+ DEFINE_TORTURE_RANDOM(tr);
u64 *wdp;
u64 *wdpp = writer_durations[me];
@@ -448,6 +450,8 @@ rcu_scale_writer(void *arg)
do {
if (writer_holdoff)
udelay(writer_holdoff);
+ if (writer_holdoff_jiffies)
+ schedule_timeout_idle(torture_random(&tr) % writer_holdoff_jiffies + 1);
wdp = &wdpp[i];
*wdp = ktime_get_mono_fast_ns();
if (gp_async) {
--
2.40.1
