Commit f8729e85 authored by Anton Blanchard's avatar Anton Blanchard Committed by Benjamin Herrenschmidt
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powerpc: Convert RTAS event scan from kernel thread to workqueue 



RTAS event scan has to run across all cpus. Right now we use a kernel
thread and set_cpus_allowed but in doing so we wake up the previous cpu
unnecessarily.

Some ftrace output shows this:

previous cpu (2):
[002]  7.022331: sched_switch: task swapper:0 [140] ==> rtasd:194 [120]
[002]  7.022338: sched_switch: task rtasd:194 [120] ==> migration/2:9 [0]
[002]  7.022344: sched_switch: task migration/2:9 [0] ==> swapper:0 [140]

next cpu (3):
[003]  7.022345: sched_switch: task swapper:0 [140] ==> rtasd:194 [120]
[003]  7.022371: sched_switch: task rtasd:194 [120] ==> swapper:0 [140]

We can use schedule_delayed_work_on and avoid the unnecessary wakeup.

Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 0512a9a8

arch/powerpc/platforms/pseries/rtasd.c

+38 −38
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ 
#include <linux/vmalloc.h>

#include <linux/spinlock.h>

#include <linux/cpu.h>

#include <linux/delay.h>

#include <linux/workqueue.h>



#include <asm/uaccess.h>

#include <asm/io.h>
@@ -387,36 +387,51 @@ static void do_event_scan(void) 
	} while(error == 0);

}



static void do_event_scan_all_cpus(long delay)

static void rtas_event_scan(struct work_struct *w);

DECLARE_DELAYED_WORK(event_scan_work, rtas_event_scan);



/*

 * Delay should be at least one second since some machines have problems if

 * we call event-scan too quickly.

 */

static unsigned long event_scan_delay = 1*HZ;

static int first_pass = 1;



static void rtas_event_scan(struct work_struct *w)

{

	int cpu;

	unsigned int cpu;



	get_online_cpus();

	cpu = first_cpu(cpu_online_map);

	for (;;) {

		set_cpus_allowed(current, cpumask_of_cpu(cpu));

	do_event_scan();

		set_cpus_allowed(current, CPU_MASK_ALL);



		/* Drop hotplug lock, and sleep for the specified delay */

		put_online_cpus();

		msleep_interruptible(delay);

	get_online_cpus();



		cpu = next_cpu(cpu, cpu_online_map);

		if (cpu == NR_CPUS)

			break;

	cpu = next_cpu(smp_processor_id(), cpu_online_map);

	if (cpu == NR_CPUS) {

		cpu = first_cpu(cpu_online_map);



		if (first_pass) {

			first_pass = 0;

			event_scan_delay = 30*HZ/rtas_event_scan_rate;



			if (surveillance_timeout != -1) {

				pr_debug("rtasd: enabling surveillance\n");

				enable_surveillance(surveillance_timeout);

				pr_debug("rtasd: surveillance enabled\n");

			}

		}

	}



	schedule_delayed_work_on(cpu, &event_scan_work,

		__round_jiffies_relative(event_scan_delay, cpu));



	put_online_cpus();

}



static int rtasd(void *unused)

static void start_event_scan(void)

{

	unsigned int err_type;

	int rc;



	daemonize("rtasd");



	printk(KERN_DEBUG "RTAS daemon started\n");

	pr_debug("rtasd: will sleep for %d milliseconds\n",

		 (30000 / rtas_event_scan_rate));
@@ -434,22 +449,8 @@ static int rtasd(void *unused) 
		}

	}



	/* First pass. */

	do_event_scan_all_cpus(1000);



	if (surveillance_timeout != -1) {

		pr_debug("rtasd: enabling surveillance\n");

		enable_surveillance(surveillance_timeout);

		pr_debug("rtasd: surveillance enabled\n");

	}



	/* Delay should be at least one second since some

	 * machines have problems if we call event-scan too

	 * quickly. */

	for (;;)

		do_event_scan_all_cpus(30000/rtas_event_scan_rate);



	return -EINVAL;

	schedule_delayed_work_on(first_cpu(cpu_online_map), &event_scan_work,

				 event_scan_delay);

}



static int __init rtas_init(void)
@@ -487,8 +488,7 @@ static int __init rtas_init(void) 
	if (!entry)

		printk(KERN_ERR "Failed to create error_log proc entry\n");



	if (kernel_thread(rtasd, NULL, CLONE_FS) < 0)

		printk(KERN_ERR "Failed to start RTAS daemon\n");

	start_event_scan();



	return 0;

}

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