File d8e5b456-qemu-no-not-require-tsc-freq-match-host.patch of Package libvirt.22291

commit d8e5b4560006590668d4669f54a46b08ec14c1a2
Author: Jiri Denemark <jdenemar@redhat.com>
Date:   Mon May 25 11:35:12 2020 +0200

    qemu: Do not require TSC frequency to strictly match host
    
    Some CPUs provide a way to read exact TSC frequency, while measuring it
    is required on other CPUs. However, measuring is never exact and the
    result may slightly differ across reboots. For this reason both Linux
    kernel and QEMU recently started allowing for guests TSC frequency to
    fall into +/- 250 ppm tolerance interval around the host TSC frequency.
    
    Let's do the same to avoid unnecessary failures (esp. during migration)
    in case the host frequency does not exactly match the frequency
    configured in a domain XML.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1839095
    
    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
    Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>

Index: libvirt-6.0.0/src/qemu/qemu_process.c
===================================================================
--- libvirt-6.0.0.orig/src/qemu/qemu_process.c
+++ libvirt-6.0.0/src/qemu/qemu_process.c
@@ -5250,12 +5250,18 @@ qemuProcessStartValidateDisks(virDomainO
 }
 
 
+/* 250 parts per million (ppm) is a half of NTP threshold */
+#define TSC_TOLERANCE 250
+
 static int
 qemuProcessStartValidateTSC(virQEMUDriverPtr driver,
                             virDomainObjPtr vm)
 {
     size_t i;
     unsigned long long freq = 0;
+    unsigned long long tolerance;
+    unsigned long long minFreq;
+    unsigned long long maxFreq;
     virHostCPUTscInfoPtr tsc;
     g_autoptr(virCPUDef) cpu = NULL;
 
@@ -5281,23 +5287,34 @@ qemuProcessStartValidateTSC(virQEMUDrive
     }
 
     tsc = cpu->tsc;
-    VIR_DEBUG("Host TSC frequency %llu Hz, scaling %s",
-              tsc->frequency, virTristateBoolTypeToString(tsc->scaling));
+    tolerance = tsc->frequency * TSC_TOLERANCE / 1000000;
+    minFreq = tsc->frequency - tolerance;
+    maxFreq = tsc->frequency + tolerance;
+
+    VIR_DEBUG("Host TSC frequency %llu Hz, scaling %s, tolerance +/- %llu Hz",
+              tsc->frequency, virTristateBoolTypeToString(tsc->scaling),
+              tolerance);
+
+    if (freq > minFreq && freq < maxFreq) {
+        VIR_DEBUG("Requested TSC frequency is within tolerance interval");
+        return 0;
+    }
 
-    if (freq == tsc->frequency || tsc->scaling == VIR_TRISTATE_BOOL_YES)
+    if (tsc->scaling == VIR_TRISTATE_BOOL_YES)
         return 0;
 
     if (tsc->scaling == VIR_TRISTATE_BOOL_ABSENT) {
-        VIR_DEBUG("TSC frequencies do not match and scaling support is "
-                  "unknown, QEMU will try and possibly fail later");
+        VIR_DEBUG("Requested TSC frequency falls outside tolerance range and "
+                  "scaling support is unknown, QEMU will try and possibly "
+                  "fail later");
         return 0;
     }
 
     virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                   _("Requested TSC frequency %llu Hz does not match "
-                     "host (%llu Hz) and TSC scaling is not supported "
-                     "by the host CPU"),
-                   freq, tsc->frequency);
+                   _("Requested TSC frequency %llu Hz is outside tolerance "
+                     "range ([%llu, %llu] Hz) around host frequency %llu Hz "
+                     "and TSC scaling is not supported by the host CPU"),
+                   freq, minFreq, maxFreq, tsc->frequency);
     return -1;
 }