[Xen-devel] [PATCH] x86/timing: Command line parameter to disable ARAT

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>

---

This has been split out of my HPET series (and hopefully for fasttract
committing) as it was only tangentially related in the first place, and has
been declared very useful.
---
 docs/misc/xen-command-line.markdown |    9 +++++++++
 xen/arch/x86/cpu/amd.c              |    2 +-
 xen/arch/x86/cpu/common.c           |    3 +++
 xen/arch/x86/cpu/cpu.h              |    1 +
 xen/arch/x86/cpu/intel.c            |    5 +++--
 5 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index dc72473..15aa404 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -155,6 +155,15 @@ to boot on systems with the following errata:
 
 Increase the verbosity of the APIC code from the default value.
 
+### arat
+> `= <boolean>`
+
+> Default: `true`
+
+Permit Xen to use "Always Running APIC Timer" support on compatible hardware
+in combination with cpuidle.  This option is only expected to be useful for
+developers wishing Xen to fall back to older timing methods on newer hardware.
+
 ### ats
 > `= <boolean>`
 
diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 27b7f71..472df68 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -502,7 +502,7 @@ static void __devinit init_amd(struct cpuinfo_x86 *c)
         * Family 0x12 and above processors have APIC timer
         * running in deep C states.
         */
-       if (c->x86 > 0x11)
+       if ( opt_arat && c->x86 > 0x11 )
                set_bit(X86_FEATURE_ARAT, c->x86_capability);
 
        /*
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index e1220e6..7e829b2 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -18,6 +18,9 @@
 static bool_t __cpuinitdata use_xsave = 1;
 boolean_param("xsave", use_xsave);
 
+bool_t __cpuinitdata opt_arat = 1;
+boolean_param("arat", opt_arat);
+
 unsigned int __devinitdata opt_cpuid_mask_ecx = ~0u;
 integer_param("cpuid_mask_ecx", opt_cpuid_mask_ecx);
 unsigned int __devinitdata opt_cpuid_mask_edx = ~0u;
diff --git a/xen/arch/x86/cpu/cpu.h b/xen/arch/x86/cpu/cpu.h
index 72c41ca..a7b7421 100644
--- a/xen/arch/x86/cpu/cpu.h
+++ b/xen/arch/x86/cpu/cpu.h
@@ -11,6 +11,7 @@ struct cpu_dev {
 
 extern struct cpu_dev * cpu_devs [X86_VENDOR_NUM];
 
+extern bool_t opt_arat;
 extern unsigned int opt_cpuid_mask_ecx, opt_cpuid_mask_edx;
 extern unsigned int opt_cpuid_mask_xsave_eax;
 extern unsigned int opt_cpuid_mask_ext_ecx, opt_cpuid_mask_ext_edx;
diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index 31b69c9..e855211 100644
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -226,8 +226,9 @@ static void __devinit init_intel(struct cpuinfo_x86 *c)
                set_bit(X86_FEATURE_NONSTOP_TSC, c->x86_capability);
                set_bit(X86_FEATURE_TSC_RELIABLE, c->x86_capability);
        }
-       if ((c->cpuid_level >= 0x00000006) &&
-           (cpuid_eax(0x00000006) & (1u<<2)))
+       if ( opt_arat &&
+            ( c->cpuid_level >= 0x00000006 ) &&
+            ( cpuid_eax(0x00000006) & (1u<<2) ) )
                set_bit(X86_FEATURE_ARAT, c->x86_capability);
 }
 
-- 
1.7.10.4


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