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x86 mmiotrace: dynamically disable non-boot CPUs

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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: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Pekka Paalanen 2008-05-12 21:21:02 +02:00 committed by Thomas Gleixner
parent 37b3619257
commit 7423d1115f
1 changed files with 61 additions and 0 deletions
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61
arch/x86/mm/mmio-mod.c
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@ -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;