[PATCH v4 4/6] x86,sched: Add support for frequency invariance on ATOM_GOLDMONT*

Giovanni Gherdovich
2019-11-13T12:41:31Z

The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
accounting. On GOLDMONT (aka Apollo Lake), GOLDMONT_D (aka Denverton) and
GOLDMONT_PLUS CPUs (aka Gemini Lake) set freq_max to the highest frequency
reported by the CPU.

The encoding of turbo ratios for GOLDMONT* is identical to the one for
SKYLAKE_X, but we treat the Atom case apart because we want to set freq_max to
a higher value, thus the ratio freq_curr/freq_max to be lower, leading to more
conservative frequency selections (favoring power efficiency).

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
---
arch/x86/kernel/smpboot.c | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0e79dcc03ae4..4d192abf337d 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1795,6 +1795,10 @@ void native_play_dead(void)
* which would ignore the entire turbo range (a conspicuous part, making
* freq_curr/freq_max always maxed out).
*
+ * An exception to the heuristic above is the Atom uarch, where we choose the
+ * highest turbo level for freq_max since Atom's are generally oriented towards
+ * power efficiency.
+ *
* Setting freq_max to anything less than the 1C turbo ratio makes the ratio
* freq_curr / freq_max to eventually grow >1, in which case we clip it to 1.
*/
@@ -1841,6 +1845,27 @@ static const struct x86_cpu_id has_glm_turbo_ratio_limits[] = {
{}
};

+static bool glm_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
+{
+ int err;
+
+ if (!x86_match_cpu(has_glm_turbo_ratio_limits))
+ return false;
+
+ err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
+ if (err)
+ return false;
+
+ err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, turbo_ratio);
+ if (err)
+ return false;
+
+ *ratio = (*ratio >> 8) & 0xFF; /* max P state ratio */
+ *turbo_ratio = *turbo_ratio & 0xFF; /* highest turbo ratio */
+
+ return true;
+}
+
static int get_knl_turbo_ratio(u64 *turbo_ratio)
{
u64 msr;
@@ -1962,7 +1987,6 @@ static void intel_set_cpu_max_freq(void)
/*
* TODO: add support for:
*
- * - Atom Goldmont
* - Atom Silvermont
*
* which all now get by default arch_max_freq = SCHED_CAPACITY_SCALE
@@ -1970,10 +1994,12 @@ static void intel_set_cpu_max_freq(void)

u64 ratio = 1, turbo_ratio = 1;

- if (turbo_disabled() ||
- x86_match_cpu(has_glm_turbo_ratio_limits))
+ if (turbo_disabled())
return;

+ if (glm_set_cpu_max_freq(&ratio, &turbo_ratio))
+ goto set_value;
+
if (knl_set_cpu_max_freq(&ratio, &turbo_ratio))
goto set_value;

--
2.16.4