[PATCH RFC 08/10] qemu_conf: Introduce a knob to turn off SCHED_CORE

[Michal Privoznik]

Ideally, we would just pick the best default and users wouldn't
have to intervene at all. But in some cases it may be handy to
not bother with SCHED_CORE at all and thus let users turn the
feature off in qemu.conf.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/libvirtd_qemu.aug         |  1 +
 src/qemu/qemu.conf.in              |  5 +++++
 src/qemu/qemu_conf.c               | 24 ++++++++++++++++++++++++
 src/qemu/qemu_conf.h               |  2 ++
 src/qemu/test_libvirtd_qemu.aug.in |  1 +
 5 files changed, 33 insertions(+)

diff --git a/src/qemu/libvirtd_qemu.aug b/src/qemu/libvirtd_qemu.aug
index 0f18775121..28a8db2b43 100644
--- a/src/qemu/libvirtd_qemu.aug
+++ b/src/qemu/libvirtd_qemu.aug
@@ -110,6 +110,7 @@ module Libvirtd_qemu =
                  | bool_entry "dump_guest_core"
                  | str_entry "stdio_handler"
                  | int_entry "max_threads_per_process"
+                 | bool_entry "sched_core"
 
    let device_entry = bool_entry "mac_filter"
                  | bool_entry "relaxed_acs_check"
diff --git a/src/qemu/qemu.conf.in b/src/qemu/qemu.conf.in
index 04b7740136..ece822edc3 100644
--- a/src/qemu/qemu.conf.in
+++ b/src/qemu/qemu.conf.in
@@ -952,3 +952,8 @@
 # DO NOT use in production.
 #
 #deprecation_behavior = "none"
+
+# If this is set then QEMU and its threads will run with SCHED_CORE set,
+# meaning no other foreign process will share Hyper Threads of a single core
+# with QEMU nor with any of its helper process.
+#sched_core = 1
diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index c22cf79cbe..03d8da0157 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -286,6 +286,8 @@ virQEMUDriverConfig *virQEMUDriverConfigNew(bool privileged,
 
     cfg->deprecationBehavior = g_strdup("none");
 
+    cfg->schedCore = virProcessSchedCoreAvailable() == 1;
+
     return g_steal_pointer(&cfg);
 }
 
@@ -634,6 +636,8 @@ virQEMUDriverConfigLoadProcessEntry(virQEMUDriverConfig *cfg,
     g_auto(GStrv) hugetlbfs = NULL;
     g_autofree char *stdioHandler = NULL;
     g_autofree char *corestr = NULL;
+    bool schedCore;
+    int rc;
     size_t i;
 
     if (virConfGetValueStringList(conf, "hugetlbfs_mount", true,
@@ -711,6 +715,26 @@ virQEMUDriverConfigLoadProcessEntry(virQEMUDriverConfig *cfg,
         }
     }
 
+    if ((rc = virConfGetValueBool(conf, "sched_core", &schedCore)) < 0) {
+        return -1;
+    } else if (rc > 0) {
+        if (schedCore) {
+            int rv = virProcessSchedCoreAvailable();
+
+            if (rv < 0) {
+                virReportSystemError(errno, "%s",
+                                     _("Unable to detect SCHED_CORE"));
+                return -1;
+            } else if (rv == 0) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("SCHED_CORE not supported by kernel"));
+                return -1;
+            }
+        }
+
+        cfg->schedCore = schedCore;
+    }
+
     return 0;
 }
 
diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index c71a666aea..32899859c0 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -223,6 +223,8 @@ struct _virQEMUDriverConfig {
     char **capabilityfilters;
 
     char *deprecationBehavior;
+
+    bool schedCore;
 };
 
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(virQEMUDriverConfig, virObjectUnref);
diff --git a/src/qemu/test_libvirtd_qemu.aug.in b/src/qemu/test_libvirtd_qemu.aug.in
index 757d21c33f..9f3f98d524 100644
--- a/src/qemu/test_libvirtd_qemu.aug.in
+++ b/src/qemu/test_libvirtd_qemu.aug.in
@@ -116,3 +116,4 @@ module Test_libvirtd_qemu =
     { "1" = "capname" }
 }
 { "deprecation_behavior" = "none" }
+{ "sched_core" = "1" }
-- 
2.35.1