Commit 7423d111 authored by Pekka Paalanen's avatar Pekka Paalanen Committed by Thomas Gleixner
Browse files

x86 mmiotrace: dynamically disable non-boot CPUs 



From 8979ee55cb6a429c4edd72ebec2244b849f6a79a Mon Sep 17 00:00:00 2001
From: Pekka Paalanen <pq@iki.fi>
Date: Sat, 12 Apr 2008 00:18:57 +0300

Mmiotrace is not reliable with multiple CPUs and may
miss events. Drop to single CPU when mmiotrace is activated.

Signed-off-by: default avatarPekka Paalanen <pq@iki.fi>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 37b36192

arch/x86/mm/mmio-mod.c

+61 −0
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ 
#include <asm/e820.h> /* for ISA_START_ADDRESS */

#include <asm/atomic.h>

#include <linux/percpu.h>

#include <linux/cpu.h>



#include "pf_in.h"
@@ -400,6 +401,64 @@ static void clear_trace_list(void) 
	}

}



#ifdef CONFIG_HOTPLUG_CPU

static cpumask_t downed_cpus;



static void enter_uniprocessor(void)

{

	int cpu;

	int err;



	get_online_cpus();

	downed_cpus = cpu_online_map;

	cpu_clear(first_cpu(cpu_online_map), downed_cpus);

	if (num_online_cpus() > 1)

		pr_notice(NAME "Disabling non-boot CPUs...\n");

	put_online_cpus();



	for_each_cpu_mask(cpu, downed_cpus) {

		err = cpu_down(cpu);

		if (!err) {

			pr_info(NAME "CPU%d is down.\n", cpu);

		} else {

			pr_err(NAME "Error taking CPU%d down: %d\n", cpu, err);

		}

	}

	if (num_online_cpus() > 1)

		pr_warning(NAME "multiple CPUs still online, "

						"may miss events.\n");

}



static void leave_uniprocessor(void)

{

	int cpu;

	int err;



	if (cpus_weight(downed_cpus) == 0)

		return;

	pr_notice(NAME "Re-enabling CPUs...\n");

	for_each_cpu_mask(cpu, downed_cpus) {

		err = cpu_up(cpu);

		if (!err)

			pr_info(NAME "enabled CPU%d.\n", cpu);

		else

			pr_err(NAME "cannot re-enable CPU%d: %d\n", cpu, err);

	}

}



#else /* !CONFIG_HOTPLUG_CPU */

static void enter_uniprocessor(void)

{

	if (num_online_cpus() > 1)

		pr_warning(NAME "multiple CPUs are online, may miss events. "

			"Suggest booting with maxcpus=1 kernel argument.\n");

}



static void leave_uniprocessor(void)

{

}

#endif



#if 0 /* XXX: out of order */

static struct file_operations fops_marker = {

	.owner =	THIS_MODULE,
@@ -422,6 +481,7 @@ void enable_mmiotrace(void) 


	if (nommiotrace)

		pr_info(NAME "MMIO tracing disabled.\n");

	enter_uniprocessor();

	spin_lock_irq(&trace_lock);

	atomic_inc(&mmiotrace_enabled);

	spin_unlock_irq(&trace_lock);
@@ -442,6 +502,7 @@ void disable_mmiotrace(void) 
	spin_unlock_irq(&trace_lock);



	clear_trace_list(); /* guarantees: no more kmmio callbacks */

	leave_uniprocessor();

	if (marker_file) {

		debugfs_remove(marker_file);

		marker_file = NULL;

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