[PATCH v2 2/2] x86/mwait-idle: add core C6 optimization for SPR

[Jan Beulich <jbeulich@xxxxxxxx>]

From: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>

Add a Sapphire Rapids Xeon C6 optimization, similar to what we have for Sky Lake
Xeon: if package C6 is disabled, adjust C6 exit latency and target residency to
match core C6 values, instead of using the default package C6 values.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
3a9cf77b60dc

Make sure a contradictory "preferred-cstates" wouldn't cause bypassing
of the added logic.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
v2: Sync with the Linux side fix to the noticed issue. Re-base over
    change to earlier patch.

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -1273,18 +1273,31 @@ static void __init skx_idle_state_table_
  */
 static void __init spr_idle_state_table_update(void)
 {
-       /* Check if user prefers C1E over C1. */
-       if (preferred_states_mask & BIT(2, U)) {
-               if (preferred_states_mask & BIT(1, U))
-                       /* Both can't be enabled, stick to the defaults. */
-                       return;
+       uint64_t msr;
 
+       /* Check if user prefers C1E over C1. */
+       if (preferred_states_mask & BIT(2, U) &&
+           !(preferred_states_mask & BIT(1, U))) {
+               /* Disable C1 and enable C1E. */
                spr_cstates[0].flags |= CPUIDLE_FLAG_DISABLED;
                spr_cstates[1].flags &= ~CPUIDLE_FLAG_DISABLED;
 
                /* Request enabling C1E using the "C1E promotion" bit. */
                idle_cpu_spr.c1e_promotion = C1E_PROMOTION_ENABLE;
        }
+
+       /*
+        * By default, the C6 state assumes the worst-case scenario of package
+        * C6. However, if PC6 is disabled, we update the numbers to match
+        * core C6.
+        */
+       rdmsrl(MSR_PKG_CST_CONFIG_CONTROL, msr);
+
+       /* Limit value 2 and above allow for PC6. */
+       if ((msr & 0x7) < 2) {
+               spr_cstates[2].exit_latency = 190;
+               spr_cstates[2].target_residency = 600;
+       }
 }
 
 /*