[Xen-devel] [PATCH 1/2] mwait_idle: Disable Baytrail Core and Module C6 auto-demotion

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

From: Len Brown <len.brown@xxxxxxxxx>

Power efficiency improves on Baytrail (Intel Atom Processor E3000)
when C6 auto-demotion is disabled.

Based on work by Srinidhi Kasagar <srinidhi.kasagar@xxxxxxxxx>.

Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 xen/arch/x86/cpu/mwait-idle.c   | 7 +++++++
 xen/include/asm-x86/msr-index.h | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/xen/arch/x86/cpu/mwait-idle.c b/xen/arch/x86/cpu/mwait-idle.c
index c2c8889..2c5864e 100644
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -88,6 +88,7 @@ struct idle_cpu {
         * Indicate which enable bits to clear here.
         */
        unsigned long auto_demotion_disable_flags;
+       bool_t byt_auto_demotion_disable_flag;
        bool_t disable_promotion_to_c1e;
 };
 
@@ -569,6 +570,7 @@ static const struct idle_cpu idle_cpu_snb = {
 static const struct idle_cpu idle_cpu_byt = {
        .state_table = byt_cstates,
        .disable_promotion_to_c1e = 1,
+       .byt_auto_demotion_disable_flag = 1,
 };
 
 static const struct idle_cpu idle_cpu_ivb = {
@@ -767,6 +769,11 @@ static int mwait_idle_cpu_init(struct notifier_block *nfb,
        if (icpu->auto_demotion_disable_flags)
                on_selected_cpus(cpumask_of(cpu), auto_demotion_disable, NULL, 
1);
 
+       if (icpu->byt_auto_demotion_disable_flag) {
+               wrmsrl(MSR_CC6_DEMOTION_POLICY_CONFIG, 0);
+               wrmsrl(MSR_MC6_DEMOTION_POLICY_CONFIG, 0);
+       }
+
        if (icpu->disable_promotion_to_c1e)
                on_selected_cpus(cpumask_of(cpu), c1e_promotion_disable, NULL, 
1);
 
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index 2056501..7e13742 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -102,6 +102,9 @@
 #define CMCI_EN                        (1UL<<30)
 #define CMCI_THRESHOLD_MASK            0x7FFF
 
+#define MSR_CC6_DEMOTION_POLICY_CONFIG 0x00000668
+#define MSR_MC6_DEMOTION_POLICY_CONFIG 0x00000669
+
 #define MSR_AMD64_MC0_MASK             0xc0010044
 
 #define MSR_IA32_MCx_CTL(x)            (MSR_IA32_MC0_CTL + 4*(x))
-- 
1.9.3


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