From: Len Brown <len.brown@xxxxxxxxx>
Reading the current frequency from PERF_STATUS
is fundamentally unreliable for multiple reasons
on multiple systems.
Indeed, one can make the case that the PERF_STATUS MSR
should be deleted from the x86 architecture due to its
ability to mis-lead.
The most common case of decpetion is P-state "hardware coordination"
that is used on all HT and multi-core processors that share
the same voltage regulator. Here the hardware runs at the speed
of the fastest sibling, and thus the "current frequency"
on the sibling that asked for a slower frequency
is erroneous 100% of the time.
For over 10 years, TM1 and TM2 have changed the frequency
out from under the system due to thermal emergencies,
without necessarily updating PERF_STATUS.
Finally, even on hardware that dutifully updates PERF_STATUS
to reflect reality, there is a race condition between software
reading the register and the changes above -- making it
fundamentally un-relaible for determining frequency.
The reliable way to determine frequency is to simply ask the
hardware how many unhalted cycles it has executed during a
known period of time via the APERF MSR. This is how
turbostat and other utilities do it...
Delete the concept of reading the current frequency from acpi-cpufreq,
and the unreliable code that is built upon it.
As the cpufreq interface has a concept of "cur" frequency,
simply return the last request. The reality is that 99% of the time
it would have got that answer from reading the hardware anway,
and so simply returning this cached value is no less accurate.
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
---
drivers/cpufreq/acpi-cpufreq.c | 201 +---------------------------------------
1 files changed, 1 insertions(+), 200 deletions(-)
diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 4e04e12..d7bd6e5 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -73,8 +73,6 @@ static struct acpi_processor_performance __percpu *acpi_perf_data;
static struct cpufreq_driver acpi_cpufreq_driver;
-static unsigned int acpi_pstate_strict;
-
static int check_est_cpu(unsigned int cpuid)
{
struct cpuinfo_x86 *cpu = &cpu_data(cpuid);
@@ -82,47 +80,6 @@ static int check_est_cpu(unsigned int cpuid)
return cpu_has(cpu, X86_FEATURE_EST);
}
-static unsigned extract_io(u32 value, struct acpi_cpufreq_data *data)
-{
- struct acpi_processor_performance *perf;
- int i;
-
- perf = data->acpi_data;
-
- for (i = 0; i < perf->state_count; i++) {
- if (value == perf->states[i].status)
- return data->freq_table[i].frequency;
- }
- return 0;
-}
-
-static unsigned extract_msr(u32 msr, struct acpi_cpufreq_data *data)
-{
- int i;
- struct acpi_processor_performance *perf;
-
- msr &= INTEL_MSR_RANGE;
- perf = data->acpi_data;
-
- for (i = 0; data->freq_table[i].frequency != CPUFREQ_TABLE_END; i++) {
- if (msr == perf->states[data->freq_table[i].index].status)
- return data->freq_table[i].frequency;
- }
- return data->freq_table[0].frequency;
-}
-
-static unsigned extract_freq(u32 val, struct acpi_cpufreq_data *data)
-{
- switch (data->cpu_feature) {
- case SYSTEM_INTEL_MSR_CAPABLE:
- return extract_msr(val, data);
- case SYSTEM_IO_CAPABLE:
- return extract_io(val, data);
- default:
- return 0;
- }
-}
-
struct msr_addr {
u32 reg;
};
@@ -142,26 +99,6 @@ struct drv_cmd {
u32 val;
};
-/* Called via smp_call_function_single(), on the target CPU */
-static void do_drv_read(void *_cmd)
-{
- struct drv_cmd *cmd = _cmd;
- u32 h;
-
- switch (cmd->type) {
- case SYSTEM_INTEL_MSR_CAPABLE:
- rdmsr(cmd->addr.msr.reg, cmd->val, h);
- break;
- case SYSTEM_IO_CAPABLE:
- acpi_os_read_port((acpi_io_address)cmd->addr.io.port,
- &cmd->val,
- (u32)cmd->addr.io.bit_width);
- break;
- default:
- break;
- }
-}
-
/* Called via smp_call_function_many(), on the target CPUs */
static void do_drv_write(void *_cmd)
{
@@ -184,15 +121,6 @@ static void do_drv_write(void *_cmd)
}
}
-static void drv_read(struct drv_cmd *cmd)
-{
- int err;
- cmd->val = 0;
-
- err = smp_call_function_any(cmd->mask, do_drv_read, cmd, 1);
- WARN_ON_ONCE(err); /* smp_call_function_any() was buggy? */
-}
-
static void drv_write(struct drv_cmd *cmd)
{
int this_cpu;
@@ -204,80 +132,6 @@ static void drv_write(struct drv_cmd *cmd)
put_cpu();
}
-static u32 get_cur_val(const struct cpumask *mask)
-{
- struct acpi_processor_performance *perf;
- struct drv_cmd cmd;
-
- if (unlikely(cpumask_empty(mask)))
- return 0;
-
- switch (per_cpu(acfreq_data, cpumask_first(mask))->cpu_feature) {
- case SYSTEM_INTEL_MSR_CAPABLE:
- cmd.type = SYSTEM_INTEL_MSR_CAPABLE;
- cmd.addr.msr.reg = MSR_IA32_PERF_STATUS;
- break;
- case SYSTEM_IO_CAPABLE:
- cmd.type = SYSTEM_IO_CAPABLE;
- perf = per_cpu(acfreq_data, cpumask_first(mask))->acpi_data;
- cmd.addr.io.port = perf->control_register.address;
- cmd.addr.io.bit_width = perf->control_register.bit_width;
- break;
- default:
- return 0;
- }
-
- cmd.mask = mask;
- drv_read(&cmd);
-
- pr_debug("get_cur_val = %u\n", cmd.val);
-
- return cmd.val;
-}
-
-static unsigned int get_cur_freq_on_cpu(unsigned int cpu)
-{
- struct acpi_cpufreq_data *data = per_cpu(acfreq_data, cpu);
- unsigned int freq;
- unsigned int cached_freq;
-
- pr_debug("get_cur_freq_on_cpu (%d)\n", cpu);
-
- if (unlikely(data == NULL ||
- data->acpi_data == NULL || data->freq_table == NULL)) {
- return 0;
- }
-
- cached_freq = data->freq_table[data->acpi_data->state].frequency;
- freq = extract_freq(get_cur_val(cpumask_of(cpu)), data);
- if (freq != cached_freq) {
- /*
- * The dreaded BIOS frequency change behind our back.
- * Force set the frequency on next target call.
- */
- data->resume = 1;
- }
-
- pr_debug("cur freq = %u\n", freq);
-
- return freq;
-}
-
-static unsigned int check_freqs(const struct cpumask *mask, unsigned int freq,
- struct acpi_cpufreq_data *data)
-{
- unsigned int cur_freq;
- unsigned int i;
-
- for (i = 0; i < 100; i++) {
- cur_freq = extract_freq(get_cur_val(mask), data);
- if (cur_freq == freq)
- return 1;
- udelay(10);
- }
- return 0;
-}
-
static int acpi_cpufreq_target(struct cpufreq_policy *policy,
unsigned int target_freq, unsigned int relation)
{
@@ -352,15 +206,6 @@ static int acpi_cpufreq_target(struct cpufreq_policy *policy,
drv_write(&cmd);
- if (acpi_pstate_strict) {
- if (!check_freqs(cmd.mask, freqs.new, data)) {
- pr_debug("acpi_cpufreq_target failed (%d)\n",
- policy->cpu);
- result = -EAGAIN;
- goto out;
- }
- }
-
for_each_cpu(i, policy->cpus) {
freqs.cpu = i;
cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
@@ -380,34 +225,6 @@ static int acpi_cpufreq_verify(struct cpufreq_policy *policy)
return cpufreq_frequency_table_verify(policy, data->freq_table);
}
-static unsigned long
-acpi_cpufreq_guess_freq(struct acpi_cpufreq_data *data, unsigned int cpu)
-{
- struct acpi_processor_performance *perf = data->acpi_data;
-
- if (cpu_khz) {
- /* search the closest match to cpu_khz */
- unsigned int i;
- unsigned long freq;
- unsigned long freqn = perf->states[0].core_frequency * 1000;
-
- for (i = 0; i < (perf->state_count-1); i++) {
- freq = freqn;
- freqn = perf->states[i+1].core_frequency * 1000;
- if ((2 * cpu_khz) > (freqn + freq)) {
- perf->state = i;
- return freq;
- }
- }
- perf->state = perf->state_count-1;
- return freqn;
- } else {
- /* assume CPU is at P0... */
- perf->state = 0;
- return perf->states[0].core_frequency * 1000;
- }
-}
-
static void free_acpi_perf_data(void)
{
unsigned int i;
@@ -638,18 +455,7 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
if (perf->states[0].core_frequency * 1000 != policy->cpuinfo.max_freq)
printk(KERN_WARNING FW_WARN "P-state 0 is not max freq\n");
- switch (perf->control_register.space_id) {
- case ACPI_ADR_SPACE_SYSTEM_IO:
- /* Current speed is unknown and not detectable by IO port */
- policy->cur = acpi_cpufreq_guess_freq(data, policy->cpu);
- break;
- case ACPI_ADR_SPACE_FIXED_HARDWARE:
- acpi_cpufreq_driver.get = get_cur_freq_on_cpu;
- policy->cur = get_cur_freq_on_cpu(cpu);
- break;
- default:
- break;
- }
+ policy->cur = data->freq_table[data->acpi_data->state].frequency;
/* notify BIOS that we exist */
acpi_processor_notify_smm(THIS_MODULE);
@@ -762,11 +568,6 @@ static void __exit acpi_cpufreq_exit(void)
free_percpu(acpi_perf_data);
}
-module_param(acpi_pstate_strict, uint, 0644);
-MODULE_PARM_DESC(acpi_pstate_strict,
- "value 0 or non-zero. non-zero -> strict ACPI checks are "
- "performed during frequency changes.");
-
late_initcall(acpi_cpufreq_init);
module_exit(acpi_cpufreq_exit);
--
1.7.5.3.367.ga9930
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