[for-next][PATCH 15/15] kernel: trace: preemptirq_delay_test: add cpu affinity

Steven Rostedt
2021-02-03T16:10:58Z

From: Song Chen <chensong_2000@189.cn>

The kernel thread executing test can run on any cpu, which might be
different cpu latency tracer is running on, as a result, the
big latency caused by preemptirq delay test can't be detected.

Therefore, the argument cpu_affinity is added to be passed to test,
ensure it's running on the same cpu with latency tracer.

e.g.
cyclictest -p 90 -m -c 0 -i 1000 -a 3
modprobe preemptirq_delay_test test_mode=preempt delay=500 \
burst_size=3 cpu_affinity=3

Link: https://lkml.kernel.org/r/1611797713-20965-1-git-send-email-chensong_2000@189.cn

Signed-off-by: Song Chen <chensong_2000@189.cn>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/Kconfig | 4 ++++
kernel/trace/preemptirq_delay_test.c | 14 ++++++++++++++
2 files changed, 18 insertions(+)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 4f976f8d9a38..799dbcfe65ad 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -886,6 +886,10 @@ config PREEMPTIRQ_DELAY_TEST
irq-disabled critical sections for 500us:
modprobe preemptirq_delay_test test_mode=irq delay=500 burst_size=3

+ What's more, if you want to attach the test on the cpu which the latency
+ tracer is running on, specify cpu_affinity=cpu_num at the end of the
+ command.
+
If unsure, say N

config SYNTH_EVENT_GEN_TEST
diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
index 312d1a0ca3b6..8c4ffd076162 100644
--- a/kernel/trace/preemptirq_delay_test.c
+++ b/kernel/trace/preemptirq_delay_test.c
@@ -21,13 +21,16 @@
static ulong delay = 100;
static char test_mode[12] = "irq";
static uint burst_size = 1;
+static int cpu_affinity = -1;

module_param_named(delay, delay, ulong, 0444);
module_param_string(test_mode, test_mode, 12, 0444);
module_param_named(burst_size, burst_size, uint, 0444);
+module_param_named(cpu_affinity, cpu_affinity, int, 0444);
MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
+MODULE_PARM_DESC(cpu_affinity, "Cpu num test is running on");

static struct completion done;

@@ -36,7 +39,9 @@ static struct completion done;
static void busy_wait(ulong time)
{
u64 start, end;
+
start = trace_clock_local();
+
do {
end = trace_clock_local();
if (kthread_should_stop())
@@ -47,6 +52,7 @@ static void busy_wait(ulong time)
static __always_inline void irqoff_test(void)
{
unsigned long flags;
+
local_irq_save(flags);
busy_wait(delay);
local_irq_restore(flags);
@@ -113,6 +119,14 @@ static int preemptirq_delay_run(void *data)
{
int i;
int s = MIN(burst_size, NR_TEST_FUNCS);
+ struct cpumask cpu_mask;
+
+ if (cpu_affinity > -1) {
+ cpumask_clear(&cpu_mask);
+ cpumask_set_cpu(cpu_affinity, &cpu_mask);
+ if (set_cpus_allowed_ptr(current, &cpu_mask))
+ pr_err("cpu_affinity:%d, failed\n", cpu_affinity);
+ }

for (i = 0; i < s; i++)
(testfuncs[i])(i);
--
2.29.2