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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.09.14 at 14:42, <ross.lagerwall@xxxxxxxxxx> wrote:
> 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>

So we raced on pulling these over - I did so late last week too and
just didn't get to send them out yet. On this one I in fact doubt
(and sent a respective query to Len; no response yet) that the MSR
handling is. Hence my ported over patch is a little different:

x86/mwait-idle: disable Baytrail Core and Module C6 auto-demotion

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

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

Signed-off-by: Len Brown <len.brown@xxxxxxxxx>

Do the MSR writes on all CPUs rather than just the current one.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -483,4 +483,7 @@
 #define _MSR_MISC_FEATURES_CPUID_FAULTING      0
 #define MSR_MISC_FEATURES_CPUID_FAULTING       (1ULL << 
_MSR_MISC_FEATURES_CPUID_FAULTING)
 
+#define MSR_CC6_DEMOTION_POLICY_CONFIG 0x00000668
+#define MSR_MC6_DEMOTION_POLICY_CONFIG 0x00000669
+
 #endif /* __ASM_MSR_INDEX_H */
--- 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;
 };
 
@@ -539,6 +540,12 @@ static void auto_demotion_disable(void *
        wrmsrl(MSR_NHM_SNB_PKG_CST_CFG_CTL, msr_bits);
 }
 
+static void byt_auto_demotion_disable(void *dummy)
+{
+       wrmsrl(MSR_CC6_DEMOTION_POLICY_CONFIG, 0);
+       wrmsrl(MSR_MC6_DEMOTION_POLICY_CONFIG, 0);
+}
+
 static void c1e_promotion_disable(void *dummy)
 {
        u64 msr_bits;
@@ -571,6 +578,7 @@ static const struct idle_cpu idle_cpu_sn
 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 = {
@@ -769,6 +777,9 @@ static int mwait_idle_cpu_init(struct no
        if (icpu->auto_demotion_disable_flags)
                on_selected_cpus(cpumask_of(cpu), auto_demotion_disable, NULL, 
1);
 
+       if (icpu->byt_auto_demotion_disable_flag)
+               on_selected_cpus(cpumask_of(cpu), byt_auto_demotion_disable, 
NULL, 1);
+
        if (icpu->disable_promotion_to_c1e)
                on_selected_cpus(cpumask_of(cpu), c1e_promotion_disable, NULL, 
1);

Attachment: x86-mwait-idle-Baytrail-no-demotion.patch
Description: Text document

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