On 16/01/2023 22.09, Nina Schoetterl-Glausch wrote:
On Thu, 2023-01-05 at 15:53 +0100, Pierre Morel wrote:
The modification of the CPU attributes are done through a monitor
commands.
It allows to move the core inside the topology tree to optimise
the cache usage in the case the host's hypervizor previously
moved the CPU.
The same command allows to modifiy the CPU attributes modifiers
like polarization entitlement and the dedicated attribute to notify
the guest if the host admin modified scheduling or dedication of a vCPU.
With this knowledge the guest has the possibility to optimize the
usage of the vCPUs.
Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
...
diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
index b69955a1cd..0faffe657e 100644
--- a/hw/s390x/cpu-topology.c
+++ b/hw/s390x/cpu-topology.c
@@ -18,6 +18,10 @@
#include "target/s390x/cpu.h"
#include "hw/s390x/s390-virtio-ccw.h"
#include "hw/s390x/cpu-topology.h"
+#include "qapi/qapi-commands-machine-target.h"
+#include "qapi/qmp/qdict.h"
+#include "monitor/hmp.h"
+#include "monitor/monitor.h"
/*
* s390_topology is used to keep the topology information.
@@ -203,6 +207,21 @@ static void s390_topology_set_entry(S390TopologyEntry *entry,
s390_topology.sockets[s390_socket_nb(id)]++;
}
+/**
+ * s390_topology_clear_entry:
+ * @entry: Topology entry to setup
+ * @id: topology id to use for the setup
+ *
+ * Clear the core bit inside the topology mask and
+ * decrements the number of cores for the socket.
+ */
+static void s390_topology_clear_entry(S390TopologyEntry *entry,
+ s390_topology_id id)
+{
+ clear_bit(63 - id.core, &entry->mask);
This doesn't take the origin into account.
+ s390_topology.sockets[s390_socket_nb(id)]--;
I suppose this function cannot run concurrently, so the same CPU doesn't get removed twice.
QEMU has the so-called BQL - the Big Qemu Lock. Instructions handlers are
normally called with the lock taken, see qemu_mutex_lock_iothread() in
target/s390x/kvm/kvm.c.
(if you feel unsure, you can add a "assert(qemu_mutex_iothread_locked())"
statement, but I think it is not necessary here)
Thomas
