Commit 2226f3dc authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcuscale: Permit blocking delays between writers 



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: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 06c2afb8

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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.

kernel/rcu/rcuscale.c

+4 −0
Original line number Diff line number Diff line
@@ -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) {