[Devel] rdmsr_on_cpu, wrmsr_on_cpu et al
Alexey Dobriyan
adobriyan at openvz.org
Wed Jan 17 05:26:13 PST 2007
Hi, Dave!
There was OpenVZ specific bug rendering some cpufreq drivers unusable
on SMP. In short, when cpufreq code thinks it confined itself to
needed cpu by means of set_cpus_allowed() to execute rdmsr, some
"virtual cpu" feature can migrate process to anywhere. This triggers
bugons and does wrong things in general.
This got fixed by introducing rdmsr_on_cpu and wrmsr_on_cpu executing
rdmsr and wrmsr on given physical cpu by means of smp_call_function_single().
So, understanding p4-clockmod is not the only driver that was affected,
is something like this acceptable for start?
arch/i386/kernel/cpu/cpufreq/Makefile | 2
arch/i386/kernel/cpu/cpufreq/msr-on-cpu.c | 71 +++++++++++++++++++++++++++++
arch/i386/kernel/cpu/cpufreq/msr-on-cpu.h | 9 +++
arch/i386/kernel/cpu/cpufreq/p4-clockmod.c | 31 ++----------
4 files changed, 88 insertions(+), 25 deletions(-)
--- a/arch/i386/kernel/cpu/cpufreq/Makefile
+++ b/arch/i386/kernel/cpu/cpufreq/Makefile
@@ -11,5 +11,5 @@ obj-$(CONFIG_X86_SPEEDSTEP_LIB) += spee
obj-$(CONFIG_X86_SPEEDSTEP_SMI) += speedstep-smi.o
obj-$(CONFIG_X86_ACPI_CPUFREQ) += acpi-cpufreq.o
obj-$(CONFIG_X86_SPEEDSTEP_CENTRINO) += speedstep-centrino.o
-obj-$(CONFIG_X86_P4_CLOCKMOD) += p4-clockmod.o
+obj-$(CONFIG_X86_P4_CLOCKMOD) += p4-clockmod.o msr-on-cpu.o
obj-$(CONFIG_X86_CPUFREQ_NFORCE2) += cpufreq-nforce2.o
--- /dev/null
+++ b/arch/i386/kernel/cpu/cpufreq/msr-on-cpu.c
@@ -0,0 +1,71 @@
+#include <linux/module.h>
+#include <linux/preempt.h>
+#include <linux/smp.h>
+#include <asm/msr.h>
+#include "msr-on-cpu.h"
+
+#ifdef CONFIG_SMP
+struct msr_info {
+ u32 msr_no;
+ u32 l, h;
+};
+
+static void __rdmsr_on_cpu(void *info)
+{
+ struct msr_info *rv = info;
+
+ rdmsr(rv->msr_no, rv->l, rv->h);
+}
+
+void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
+{
+ preempt_disable();
+ if (smp_processor_id() == cpu)
+ rdmsr(msr_no, *l, *h);
+ else {
+ struct msr_info rv;
+
+ rv.msr_no = msr_no;
+ smp_call_function_single(cpu, __rdmsr_on_cpu, &rv, 0, 1);
+ *l = rv.l;
+ *h = rv.h;
+ }
+ preempt_enable();
+}
+
+static void __wrmsr_on_cpu(void *info)
+{
+ struct msr_info *rv = info;
+
+ wrmsr(rv->msr_no, rv->l, rv->h);
+}
+
+void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
+{
+ preempt_disable();
+ if (smp_processor_id() == cpu)
+ wrmsr(msr_no, l, h);
+ else {
+ struct msr_info rv;
+
+ rv.msr_no = msr_no;
+ rv.l = l;
+ rv.h = h;
+ smp_call_function_single(cpu, __wrmsr_on_cpu, &rv, 0, 1);
+ }
+ preempt_enable();
+}
+#else
+void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
+{
+ rdmsr(msr_no, *l, *h);
+}
+
+void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
+{
+ wrmsr(msr_no, l, h);
+}
+#endif
+
+EXPORT_SYMBOL(rdmsr_on_cpu);
+EXPORT_SYMBOL(wrmsr_on_cpu);
--- /dev/null
+++ b/arch/i386/kernel/cpu/cpufreq/msr-on-cpu.h
@@ -0,0 +1,9 @@
+#ifndef __MSR_ON_CPU_H__
+#define __MSR_ON_CPU_H__
+
+#include <linux/types.h>
+
+void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
+void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h);
+
+#endif
--- a/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c
+++ b/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c
@@ -33,6 +33,7 @@ #include <asm/processor.h>
#include <asm/msr.h>
#include <asm/timex.h>
+#include "msr-on-cpu.h"
#include "speedstep-lib.h"
#define PFX "p4-clockmod: "
@@ -63,7 +64,7 @@ static int cpufreq_p4_setdc(unsigned int
if (!cpu_online(cpu) || (newstate > DC_DISABLE) || (newstate == DC_RESV))
return -EINVAL;
- rdmsr(MSR_IA32_THERM_STATUS, l, h);
+ rdmsr_on_cpu(cpu, MSR_IA32_THERM_STATUS, &l, &h);
if (l & 0x01)
dprintk("CPU#%d currently thermal throttled\n", cpu);
@@ -71,10 +72,10 @@ static int cpufreq_p4_setdc(unsigned int
if (has_N44_O17_errata[cpu] && (newstate == DC_25PT || newstate == DC_DFLT))
newstate = DC_38PT;
- rdmsr(MSR_IA32_THERM_CONTROL, l, h);
+ rdmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, &l, &h);
if (newstate == DC_DISABLE) {
dprintk("CPU#%d disabling modulation\n", cpu);
- wrmsr(MSR_IA32_THERM_CONTROL, l & ~(1<<4), h);
+ wrmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, l & ~(1<<4), h);
} else {
dprintk("CPU#%d setting duty cycle to %d%%\n",
cpu, ((125 * newstate) / 10));
@@ -85,7 +86,7 @@ static int cpufreq_p4_setdc(unsigned int
*/
l = (l & ~14);
l = l | (1<<4) | ((newstate & 0x7)<<1);
- wrmsr(MSR_IA32_THERM_CONTROL, l, h);
+ wrmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, l, h);
}
return 0;
@@ -112,7 +113,6 @@ static int cpufreq_p4_target(struct cpuf
{
unsigned int newstate = DC_RESV;
struct cpufreq_freqs freqs;
- cpumask_t cpus_allowed;
int i;
if (cpufreq_frequency_table_target(policy, &p4clockmod_table[0], target_freq, relation, &newstate))
@@ -133,17 +133,8 @@ static int cpufreq_p4_target(struct cpuf
/* run on each logical CPU, see section 13.15.3 of IA32 Intel Architecture Software
* Developer's Manual, Volume 3
*/
- cpus_allowed = current->cpus_allowed;
-
- for_each_cpu_mask(i, policy->cpus) {
- cpumask_t this_cpu = cpumask_of_cpu(i);
-
- set_cpus_allowed(current, this_cpu);
- BUG_ON(smp_processor_id() != i);
-
+ for_each_cpu_mask(i, policy->cpus)
cpufreq_p4_setdc(i, p4clockmod_table[newstate].index);
- }
- set_cpus_allowed(current, cpus_allowed);
/* notifiers */
for_each_cpu_mask(i, policy->cpus) {
@@ -265,17 +256,9 @@ static int cpufreq_p4_cpu_exit(struct cp
static unsigned int cpufreq_p4_get(unsigned int cpu)
{
- cpumask_t cpus_allowed;
u32 l, h;
- cpus_allowed = current->cpus_allowed;
-
- set_cpus_allowed(current, cpumask_of_cpu(cpu));
- BUG_ON(smp_processor_id() != cpu);
-
- rdmsr(MSR_IA32_THERM_CONTROL, l, h);
-
- set_cpus_allowed(current, cpus_allowed);
+ rdmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, &l, &h);
if (l & 0x10) {
l = l >> 1;
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