[Xen-devel] [PATCH 2/3] x86/mwait_idle: export both C1 and C1E

["Jan Beulich" <JBeulich@xxxxxxxx>]

Here we disable HW promotion of C1 to C1E and export both C1 and C1E
as distinct C-states.

This allows a cpuidle governor to choose a lower latency C-state than
C1E when necessary to satisfy performance and QOS constraints -- and
still save power versus polling.
This also corrects the erroneous latency previously reported for C1E
-- it is 10usec, not 1usec.

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

Avoided the effect of changing the meaning of "max_cstate=".

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

--- 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 disable_promotion_to_c1e;
 };
 
 static const struct idle_cpu *icpu;
@@ -132,6 +133,12 @@ static const struct cpuidle_state nehale
                .target_residency = 6,
        },
        {
+               .name = "C1E-NHM",
+               .flags = MWAIT2flg(0x01),
+               .exit_latency = 10,
+               .target_residency = 20,
+       },
+       {
                .name = "C3-NHM",
                .flags = MWAIT2flg(0x10) | CPUIDLE_FLAG_TLB_FLUSHED,
                .exit_latency = 20,
@@ -150,8 +157,14 @@ static const struct cpuidle_state snb_cs
        {
                .name = "C1-SNB",
                .flags = MWAIT2flg(0x00),
-               .exit_latency = 1,
-               .target_residency = 1,
+               .exit_latency = 2,
+               .target_residency = 2,
+       },
+       {
+               .name = "C1E-SNB",
+               .flags = MWAIT2flg(0x01),
+               .exit_latency = 10,
+               .target_residency = 20,
        },
        {
                .name = "C3-SNB",
@@ -182,6 +195,12 @@ static const struct cpuidle_state ivb_cs
                .target_residency = 1,
        },
        {
+               .name = "C1E-IVB",
+               .flags = MWAIT2flg(0x01),
+               .exit_latency = 10,
+               .target_residency = 20,
+       },
+       {
                .name = "C3-IVB",
                .flags = MWAIT2flg(0x10) | CPUIDLE_FLAG_TLB_FLUSHED,
                .exit_latency = 59,
@@ -210,6 +229,12 @@ static const struct cpuidle_state hsw_cs
                .target_residency = 2,
        },
        {
+               .name = "C1E-HSW",
+               .flags = MWAIT2flg(0x01),
+               .exit_latency = 10,
+               .target_residency = 20,
+       },
+       {
                .name = "C3-HSW",
                .flags = MWAIT2flg(0x10) | CPUIDLE_FLAG_TLB_FLUSHED,
                .exit_latency = 33,
@@ -232,10 +257,10 @@ static const struct cpuidle_state hsw_cs
 
 static const struct cpuidle_state atom_cstates[] = {
        {
-               .name = "C1-ATM",
+               .name = "C1E-ATM",
                .flags = MWAIT2flg(0x00),
-               .exit_latency = 1,
-               .target_residency = 4,
+               .exit_latency = 10,
+               .target_residency = 20,
        },
        {
                .name = "C2-ATM",
@@ -354,9 +379,19 @@ static void auto_demotion_disable(void *
        wrmsrl(MSR_NHM_SNB_PKG_CST_CFG_CTL, msr_bits);
 }
 
+static void c1e_promotion_disable(void *dummy)
+{
+       u64 msr_bits;
+
+       rdmsrl(MSR_IA32_POWER_CTL, msr_bits);
+       msr_bits &= ~0x2;
+       wrmsrl(MSR_IA32_POWER_CTL, msr_bits);
+}
+
 static const struct idle_cpu idle_cpu_nehalem = {
        .state_table = nehalem_cstates,
        .auto_demotion_disable_flags = NHM_C1_AUTO_DEMOTE | NHM_C3_AUTO_DEMOTE,
+       .disable_promotion_to_c1e = 1,
 };
 
 static const struct idle_cpu idle_cpu_atom = {
@@ -370,14 +405,17 @@ static const struct idle_cpu idle_cpu_li
 
 static const struct idle_cpu idle_cpu_snb = {
        .state_table = snb_cstates,
+       .disable_promotion_to_c1e = 1,
 };
 
 static const struct idle_cpu idle_cpu_ivb = {
        .state_table = ivb_cstates,
+       .disable_promotion_to_c1e = 1,
 };
 
 static const struct idle_cpu idle_cpu_hsw = {
        .state_table = hsw_cstates,
+       .disable_promotion_to_c1e = 1,
 };
 
 #define ICPU(model, cpu) { 6, model, &idle_cpu_##cpu }
@@ -520,6 +558,9 @@ 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->disable_promotion_to_c1e)
+               on_selected_cpus(cpumask_of(cpu), c1e_promotion_disable, NULL, 
1);
+
        return NOTIFY_DONE;
 }
 
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -83,6 +83,8 @@
 #define MSR_IA32_LASTINTFROMIP         0x000001dd
 #define MSR_IA32_LASTINTTOIP           0x000001de
 
+#define MSR_IA32_POWER_CTL             0x000001fc
+
 #define MSR_IA32_MTRR_PHYSBASE0     0x00000200
 #define MSR_IA32_MTRR_PHYSMASK0     0x00000201
 #define MSR_IA32_MTRR_PHYSBASE1     0x00000202

Attachment: x86-mwait-idle-C1E.patch
Description: Text document

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