[Xen-devel] [PATCH 5/5] mwait-idle: correct/improve BXT support

["Jan Beulich" <JBeulich@xxxxxxxx>]

Linux commit 5dcef69486 ("intel_idle: add BXT support") added an
8-element lookup array with just a 2-bit value used for lookups. As per
the SDM that bit field is really 3 bits wide. Since the top two array
entries are zero, deal with the resulting invalid (zero) values by
moving the zero-MSR-value check into irtl_2_usec() and having that
function's caller check its result instead.

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

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -922,7 +922,10 @@ static unsigned long long __init irtl_2_
 {
        unsigned long long ns;
 
-       ns = irtl_ns_units[(irtl >> 10) & 0x3];
+       if (!irtl)
+               return 0;
+
+       ns = irtl_ns_units[(irtl >> 10) & 0x7];
 
        return (irtl & 0x3FF) * ns / 1000;
 }
@@ -935,43 +938,39 @@ static unsigned long long __init irtl_2_
 static void __init bxt_idle_state_table_update(void)
 {
        unsigned long long msr;
+       unsigned int usec;
 
        rdmsrl(MSR_PKGC6_IRTL, msr);
-       if (msr) {
-               unsigned int usec = irtl_2_usec(msr);
-
+       usec = irtl_2_usec(msr);
+       if (usec) {
                bxt_cstates[2].exit_latency = usec;
                bxt_cstates[2].target_residency = usec;
        }
 
        rdmsrl(MSR_PKGC7_IRTL, msr);
-       if (msr) {
-               unsigned int usec = irtl_2_usec(msr);
-
+       usec = irtl_2_usec(msr);
+       if (usec) {
                bxt_cstates[3].exit_latency = usec;
                bxt_cstates[3].target_residency = usec;
        }
 
        rdmsrl(MSR_PKGC8_IRTL, msr);
-       if (msr) {
-               unsigned int usec = irtl_2_usec(msr);
-
+       usec = irtl_2_usec(msr);
+       if (usec) {
                bxt_cstates[4].exit_latency = usec;
                bxt_cstates[4].target_residency = usec;
        }
 
        rdmsrl(MSR_PKGC9_IRTL, msr);
-       if (msr) {
-               unsigned int usec = irtl_2_usec(msr);
-
+       usec = irtl_2_usec(msr);
+       if (usec) {
                bxt_cstates[5].exit_latency = usec;
                bxt_cstates[5].target_residency = usec;
        }
 
        rdmsrl(MSR_PKGC10_IRTL, msr);
-       if (msr) {
-               unsigned int usec = irtl_2_usec(msr);
-
+       usec = irtl_2_usec(msr);
+       if (usec) {
                bxt_cstates[6].exit_latency = usec;
                bxt_cstates[6].target_residency = usec;
        }

Attachment: x86-mwait-idle-BXT-time-unit.patch
Description: Text document

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