Messages in this thread Patch in this message | | | Date | Thu, 24 Apr 2008 22:39:47 +0300 | From | Pekka Paalanen <> | Subject | [PATCH v2] 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 Subject: [PATCH] x86 mmiotrace: dynamically disable non-boot CPUs
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> ---
I've tested this patch on my Core 2 Duo laptop, and with "[PATCH v2] Check for breakpoint in text_poke to eliminate bug_on" cpu hotplug seems to work fine on a sched-devel/latest SMP kernel both with and without CONFIG_HOTPLUG_CPU.
One strange thing was a stack trace printed just before the CPU resets for "shutdown -r now", but I could not see what it was about. I'll ignore that for now, hopefully it's something unrelated.
arch/x86/mm/mmio-mod.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 61 insertions(+), 0 deletions(-)
diff --git a/arch/x86/mm/mmio-mod.c b/arch/x86/mm/mmio-mod.c index 6d6cac8..1f77d85 100644 --- a/arch/x86/mm/mmio-mod.c +++ b/arch/x86/mm/mmio-mod.c @@ -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; -- 1.5.3.7
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