On Fri, Jan 17, 2020 at 04:58:14PM -0500, Joel Fernandes wrote:
> Hi,
> Me and Daniel were poking around with RCU_BOOST. I wrote a kernel module to
> test it a bit and I don't see the boost happening (thanks to Daniel for idea
> of writing a module). Haven't debugged it more yet. Will look more tomorrow.
> But below is the kernel module code and it prints a FAIL message to kernel
> logs in a few seconds.
>
> I see the reader thread not getting CPU for several seconds. RCU_BOOST_DELAY
> is set to 500.
>
> Thoughts?
So this could be because I did not start a grace period which is quite silly.
I am sorry about that. I will add another thread to start grace periods as
well and let you know if I still see a problem.
thanks,
- Joel
>
> ---8<-----------------------
>
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index c1860d35dc7e..ba34957dff26 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -2,7 +2,7 @@
> #
> # Makefile for misc devices that really don't fit anywhere else.
> #
> -
> +obj-m += ptest.o
> obj-$(CONFIG_IBM_ASM) += ibmasm/
> obj-$(CONFIG_IBMVMC) += ibmvmc.o
> obj-$(CONFIG_AD525X_DPOT) += ad525x_dpot.o
> diff --git a/drivers/misc/ptest.c b/drivers/misc/ptest.c
> new file mode 100644
> index 000000000000..76cc9524ccac
> --- /dev/null
> +++ b/drivers/misc/ptest.c
> @@ -0,0 +1,112 @@
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/vmalloc.h>
> +#include <linux/kthread.h>
> +#include <linux/delay.h>
> +
> +#define RCU_READER_DELAY 100 //ms
> +#define RCU_BLOCKER_DELAY 600 //ms
> +
> +MODULE_LICENSE("GPL");
> +
> +struct sched_param {
> + int sched_priority;
> +};
> +
> +int stop_test = 0;
> +int test_pass = 1;
> +int reader_exit = 0;
> +s64 delta_fail;
> +
> +#define ns_to_ms(delta) (delta / 1000000ULL)
> +
> +static int rcu_reader(void *a)
> +{
> + ktime_t start, end, reader_begin;
> + s64 delta;
> +
> + reader_begin = ktime_get();
> +
> + while (!kthread_should_stop() && !stop_test) {
> + start = ktime_get();
> + rcu_read_lock();
> + trace_printk("rcu_reader entering RSCS\n");
> + mdelay(RCU_READER_DELAY);
> + trace_printk("rcu_reader exiting RSCS\n");
> + rcu_read_lock();
> + end = ktime_get();
> + delta = ktime_to_ns(ktime_sub(end, start));
> +
> + if (delta < 0 || (ns_to_ms(delta) > (2 * RCU_READER_DELAY))) {
> + delta_fail = delta;
> + test_pass = 0;
> + break;
> + }
> +
> + // Don't let the rcu_reader() run more than 3s inorder to
> + // not starve the blocker incase reader prio > blocker prio.
> + delta = ktime_to_ns(ktime_sub(end, reader_begin));
> + if (ns_to_ms(delta) > 3000)
> + break;
> + }
> +
> + stop_test = 1;
> + reader_exit = 1;
> + pr_err("Exiting reader\n");
> + return 0;
> +}
> +
> +static int rcu_blocker(void *a)
> +{
> + int loops = 5;
> +
> + while (!kthread_should_stop() && loops-- && !stop_test) {
> + trace_printk("rcu_blocker entering\n");
> + mdelay(RCU_BLOCKER_DELAY);
> + trace_printk("rcu_blocker exiting\n");
> + }
> +
> + pr_err("Exiting blocker\n");
> + stop_test = 1;
> +
> + // Wait for reader to finish
> + while (!reader_exit)
> + schedule_timeout_uninterruptible(1);
> +
> + if (test_pass)
> + pr_err("TEST PASSED\n");
> + else
> + pr_err("TEST FAILED, failing delta=%lldms\n", ns_to_ms(delta_fail));
> +
> + return 0;
> +}
> +
> +static int __init ptest_init(void){
> + struct sched_param params;
> + struct task_struct *reader, *blocker;
> +
> + reader = kthread_create(rcu_reader, NULL, "reader");
> + params.sched_priority = 50;
> + sched_setscheduler(reader, SCHED_FIFO, ¶ms);
> + kthread_bind(reader, smp_processor_id());
> +
> + blocker = kthread_create(rcu_blocker, NULL, "blocker");
> + params.sched_priority = 60;
> + sched_setscheduler(blocker, SCHED_FIFO, ¶ms);
> + kthread_bind(blocker, smp_processor_id());
> +
> + wake_up_process(reader);
> +
> + // Let reader run a little
> + mdelay(50);
> +
> + wake_up_process(blocker);
> + return 0;
> +}
> +
> +static void __exit ptest_exit(void){
> +}
> +
> +module_init(ptest_init);
> +module_exit(ptest_exit);
> --
> 2.25.0.341.g760bfbb309-goog
>
