[tip: sched/core] x86, sched: Add support for frequency invariance on ATOM_GOLDMONT*

[tip-bot2 for Giovanni Gherdovich]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     eacf0474aec8bdccdc7f19386319127c67be3588
Gitweb:        https://git.kernel.org/tip/eacf0474aec8bdccdc7f19386319127c67be3588
Author:        Giovanni Gherdovich <ggherdovich@xxxxxxx>
AuthorDate:    Wed, 22 Jan 2020 16:16:15 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 28 Jan 2020 21:37:04 +01:00

x86, sched: Add support for frequency invariance on ATOM_GOLDMONT*

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@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20200122151617.531-5-ggherdovich@xxxxxxx
---
 arch/x86/kernel/smpboot.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 8cb3113..3e32d62 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.
  */
@@ -1937,18 +1941,18 @@ static bool intel_set_max_freq_ratio(void)
 	/*
 	 * TODO: add support for:
 	 *
-	 * - Atom Goldmont
 	 * - Atom Silvermont
 	 */
 
 	u64 base_freq = 1, turbo_freq = 1;
 
-	if (x86_match_cpu(has_glm_turbo_ratio_limits))
-		return false;
-
 	if (turbo_disabled())
 		goto out;
 
+	if (x86_match_cpu(has_glm_turbo_ratio_limits) &&
+	    skx_set_max_freq_ratio(&base_freq, &turbo_freq, 1))
+		goto out;
+
 	if (knl_set_max_freq_ratio(&base_freq, &turbo_freq, 1))
 		goto out;