On Thursday, February 24, 2022 9:08:30 AM CET Feng Tang wrote:
> On Wed, Feb 23, 2022 at 03:23:20PM +0100, Rafael J. Wysocki wrote:
> > On Wed, Feb 23, 2022 at 1:40 AM Feng Tang <feng.tang@xxxxxxxxx> wrote:
> > >
> > > On Tue, Feb 22, 2022 at 04:32:29PM -0800, srinivas pandruvada wrote:
> > > > Hi Doug,
> > > >
> > > > On Tue, 2022-02-22 at 16:07 -0800, Doug Smythies wrote:
> > > > > Hi All,
> > > > >
> > > > > I am about 1/2 way through testing Feng's "hacky debug patch",
> > > > > let me know if I am wasting my time, and I'll abort. So far, it
> > > > > works fine.
> > > > This just proves that if you add some callback during long idle, you
> > > > will reach a less aggressive p-state. I think you already proved that
> > > > with your results below showing 1W less average power ("Kernel 5.17-rc3
> > > > + Feng patch (6 samples at 300 sec per").
> > > >
> > > > Rafael replied with one possible option. Alternatively when planing to
> > > > enter deep idle, set P-state to min with a callback like we do in
> > > > offline callback.
> > >
> > > Yes, if the system is going to idle, it makes sense to goto a lower
> > > cpufreq first (also what my debug patch will essentially lead to).
> > >
> > > Given cprfreq-util's normal running frequency is every 10ms, doing
> > > this before entering idle is not a big extra burden.
> >
> > But this is not related to idle as such, but to the fact that idle
> > sometimes stops the scheduler tick which otherwise would run the
> > cpufreq governor callback on a regular basis.
> >
> > It is stopping the tick that gets us into trouble, so I would avoid
> > doing it if the current performance state is too aggressive.
>
> I've tried to simulate Doug's environment by using his kconfig, and
> offline my 36 CPUs Desktop to leave 12 CPUs online, and on it I can
> still see Local timer interrupts when there is no active load, with
> the longest interval between 2 timer interrupts is 4 seconds, while
> idle class's task_tick_idle() will do nothing, and CFS'
> task_tick_fair() will in turn call cfs_rq_util_change()
>
> I searched the cfs/deadline/rt code, these three classes all have
> places to call cpufreq_update_util(), either in enqueue/dequeue or
> changing running bandwidth. So I think entering idle also means the
> system load is under a big change, and worth calling the cpufreq
> callback.
>
> > In principle, PM QoS can be used for that from intel_pstate, but there
> > is a problem with that approach, because it is not obvious what value
> > to give to it and it is not always guaranteed to work (say when all of
> > the C-states except for C1 are disabled).
> >
> > So it looks like a new mechanism is needed for that.
>
> If you think idle class is not the right place to solve it, I can
> also help testing new patches.
So I have the appended experimental patch to address this issue that's not
been tested at all. Caveat emptor.
I've been looking for something relatively low-overhead and taking all of the
dependencies into account.
---
drivers/cpufreq/intel_pstate.c | 40 ++++++++++++++++++++++++++++---------
drivers/cpuidle/governors/ladder.c | 6 +++--
drivers/cpuidle/governors/menu.c | 2 +
drivers/cpuidle/governors/teo.c | 3 ++
include/linux/cpuidle.h | 4 +++
5 files changed, 44 insertions(+), 11 deletions(-)
Index: linux-pm/drivers/cpuidle/governors/menu.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/menu.c
+++ linux-pm/drivers/cpuidle/governors/menu.c
@@ -284,6 +284,8 @@ static int menu_select(struct cpuidle_dr
if (unlikely(delta < 0)) {
delta = 0;
delta_tick = 0;
+ } else if (dev->retain_tick) {
+ delta = delta_tick;
}
data->next_timer_ns = delta;
Index: linux-pm/drivers/cpuidle/governors/teo.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/teo.c
+++ linux-pm/drivers/cpuidle/governors/teo.c
@@ -308,6 +308,9 @@ static int teo_select(struct cpuidle_dri
cpu_data->time_span_ns = local_clock();
duration_ns = tick_nohz_get_sleep_length(&delta_tick);
+ if (dev->retain_tick)
+ duration_ns = delta_tick;
+
cpu_data->sleep_length_ns = duration_ns;
/* Check if there is any choice in the first place. */
Index: linux-pm/include/linux/cpuidle.h
===================================================================
--- linux-pm.orig/include/linux/cpuidle.h
+++ linux-pm/include/linux/cpuidle.h
@@ -93,6 +93,7 @@ struct cpuidle_device {
unsigned int registered:1;
unsigned int enabled:1;
unsigned int poll_time_limit:1;
+ unsigned int retain_tick:1;
unsigned int cpu;
ktime_t next_hrtimer;
@@ -172,6 +173,8 @@ extern int cpuidle_play_dead(void);
extern struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev);
static inline struct cpuidle_device *cpuidle_get_device(void)
{return __this_cpu_read(cpuidle_devices); }
+
+extern void cpuidle_update_retain_tick(bool val);
#else
static inline void disable_cpuidle(void) { }
static inline bool cpuidle_not_available(struct cpuidle_driver *drv,
@@ -211,6 +214,7 @@ static inline int cpuidle_play_dead(void
static inline struct cpuidle_driver *cpuidle_get_cpu_driver(
struct cpuidle_device *dev) {return NULL; }
static inline struct cpuidle_device *cpuidle_get_device(void) {return NULL; }
+static inline void cpuidle_update_retain_tick(bool val) { }
#endif
#ifdef CONFIG_CPU_IDLE
Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -19,6 +19,7 @@
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/cpufreq.h>
+#include <linux/cpuidle.h>
#include <linux/sysfs.h>
#include <linux/types.h>
#include <linux/fs.h>
@@ -1970,6 +1971,30 @@ static inline void intel_pstate_cppc_set
}
#endif /* CONFIG_ACPI_CPPC_LIB */
+static void intel_pstate_update_perf_ctl(struct cpudata *cpu)
+{
+ int pstate = cpu->pstate.current_pstate;
+
+ /*
+ * Avoid stopping the scheduler tick from cpuidle on CPUs in turbo
+ * P-states to prevent them from getting back to the high frequency
+ * right away after getting out of deep idle.
+ */
+ cpuidle_update_retain_tick(pstate > cpu->pstate.max_pstate);
+ wrmsrl(MSR_IA32_PERF_CTL, pstate_funcs.get_val(cpu, pstate));
+}
+
+static void intel_pstate_update_perf_ctl_wrapper(void *cpu_data)
+{
+ intel_pstate_update_perf_ctl(cpu_data);
+}
+
+static void intel_pstate_update_perf_ctl_on_cpu(struct cpudata *cpu)
+{
+ smp_call_function_single(cpu->cpu, intel_pstate_update_perf_ctl_wrapper,
+ cpu, 1);
+}
+
static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
{
trace_cpu_frequency(pstate * cpu->pstate.scaling, cpu->cpu);
@@ -1979,8 +2004,7 @@ static void intel_pstate_set_pstate(stru
* the CPU being updated, so force the register update to run on the
* right CPU.
*/
- wrmsrl_on_cpu(cpu->cpu, MSR_IA32_PERF_CTL,
- pstate_funcs.get_val(cpu, pstate));
+ intel_pstate_update_perf_ctl_on_cpu(cpu);
}
static void intel_pstate_set_min_pstate(struct cpudata *cpu)
@@ -2256,7 +2280,7 @@ static void intel_pstate_update_pstate(s
return;
cpu->pstate.current_pstate = pstate;
- wrmsrl(MSR_IA32_PERF_CTL, pstate_funcs.get_val(cpu, pstate));
+ intel_pstate_update_perf_ctl(cpu);
}
static void intel_pstate_adjust_pstate(struct cpudata *cpu)
@@ -2843,11 +2867,9 @@ static void intel_cpufreq_perf_ctl_updat
u32 target_pstate, bool fast_switch)
{
if (fast_switch)
- wrmsrl(MSR_IA32_PERF_CTL,
- pstate_funcs.get_val(cpu, target_pstate));
+ intel_pstate_update_perf_ctl(cpu);
else
- wrmsrl_on_cpu(cpu->cpu, MSR_IA32_PERF_CTL,
- pstate_funcs.get_val(cpu, target_pstate));
+ intel_pstate_update_perf_ctl_on_cpu(cpu);
}
static int intel_cpufreq_update_pstate(struct cpufreq_policy *policy,
@@ -2857,6 +2879,8 @@ static int intel_cpufreq_update_pstate(s
int old_pstate = cpu->pstate.current_pstate;
target_pstate = intel_pstate_prepare_request(cpu, target_pstate);
+ cpu->pstate.current_pstate = target_pstate;
+
if (hwp_active) {
int max_pstate = policy->strict_target ?
target_pstate : cpu->max_perf_ratio;
@@ -2867,8 +2891,6 @@ static int intel_cpufreq_update_pstate(s
intel_cpufreq_perf_ctl_update(cpu, target_pstate, fast_switch);
}
- cpu->pstate.current_pstate = target_pstate;
-
intel_cpufreq_trace(cpu, fast_switch ? INTEL_PSTATE_TRACE_FAST_SWITCH :
INTEL_PSTATE_TRACE_TARGET, old_pstate);
Index: linux-pm/drivers/cpuidle/governors/ladder.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/ladder.c
+++ linux-pm/drivers/cpuidle/governors/ladder.c
@@ -61,10 +61,10 @@ static inline void ladder_do_selection(s
* ladder_select_state - selects the next state to enter
* @drv: cpuidle driver
* @dev: the CPU
- * @dummy: not used
+ * @stop_tick: Whether or not to stop the scheduler tick
*/
static int ladder_select_state(struct cpuidle_driver *drv,
- struct cpuidle_device *dev, bool *dummy)
+ struct cpuidle_device *dev, bool *stop_tick)
{
struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
struct ladder_device_state *last_state;
@@ -73,6 +73,8 @@ static int ladder_select_state(struct cp
s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
s64 last_residency;
+ *stop_tick = !dev->retain_tick;
+
/* Special case when user has set very strict latency requirement */
if (unlikely(latency_req == 0)) {
ladder_do_selection(dev, ldev, last_idx, 0);
