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Re: [PATCH v10 1/9] s390x/cpu topology: core_id sets s390x CPU topology


From: Cédric Le Goater
Subject: Re: [PATCH v10 1/9] s390x/cpu topology: core_id sets s390x CPU topology
Date: Mon, 24 Oct 2022 11:22:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0

On 10/19/22 17:39, Pierre Morel wrote:


On 10/18/22 18:43, Cédric Le Goater wrote:
Hello Pierre,

On 10/12/22 18:20, Pierre Morel wrote:
In the S390x CPU topology the core_id specifies the CPU address
and the position of the core withing the topology.

Let's build the topology based on the core_id.
s390x/cpu topology: core_id sets s390x CPU topology

In the S390x CPU topology the core_id specifies the CPU address
and the position of the cpu withing the topology.

Let's build the topology based on the core_id.

The commit log is doubled.

Yes, thanks.



Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
  include/hw/s390x/cpu-topology.h |  45 +++++++++++
  hw/s390x/cpu-topology.c         | 132 ++++++++++++++++++++++++++++++++
  hw/s390x/s390-virtio-ccw.c      |  21 +++++
  hw/s390x/meson.build            |   1 +
  4 files changed, 199 insertions(+)
  create mode 100644 include/hw/s390x/cpu-topology.h
  create mode 100644 hw/s390x/cpu-topology.c

diff --git a/include/hw/s390x/cpu-topology.h b/include/hw/s390x/cpu-topology.h
new file mode 100644
index 0000000000..66c171d0bc
--- /dev/null
+++ b/include/hw/s390x/cpu-topology.h
@@ -0,0 +1,45 @@
+/*
+ * CPU Topology
+ *
+ * Copyright 2022 IBM Corp.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+#ifndef HW_S390X_CPU_TOPOLOGY_H
+#define HW_S390X_CPU_TOPOLOGY_H
+
+#include "hw/qdev-core.h"
+#include "qom/object.h"
+
+typedef struct S390TopoContainer {
+    int active_count;
+} S390TopoContainer;

This structure does not seem very useful.

+
+#define S390_TOPOLOGY_CPU_IFL 0x03
+#define S390_TOPOLOGY_MAX_ORIGIN ((63 + S390_MAX_CPUS) / 64)
+typedef struct S390TopoTLE {

The 'Topo' is redundant as TLE stands for 'topology-list entry'. This is minor.

+    uint64_t mask[S390_TOPOLOGY_MAX_ORIGIN];
+} S390TopoTLE;
+
+struct S390Topology {
+    SysBusDevice parent_obj;
+    int cpus;
+    S390TopoContainer *socket;
+    S390TopoTLE *tle;
+    MachineState *ms;

hmm, it would be cleaner to introduce the fields and properties needed
by the S390Topology model and avoid dragging the machine object pointer.
AFAICT, these properties would be :

   "nr-cpus"
   "max-cpus"
   "nr-sockets"


OK



+};
+
+#define TYPE_S390_CPU_TOPOLOGY "s390-topology"
+OBJECT_DECLARE_SIMPLE_TYPE(S390Topology, S390_CPU_TOPOLOGY)
+
+S390Topology *s390_get_topology(void);
+void s390_topology_new_cpu(int core_id);
+
+static inline bool s390_has_topology(void)
+{
+    return false;
+}
+
+#endif
diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
new file mode 100644
index 0000000000..42b22a1831
--- /dev/null
+++ b/hw/s390x/cpu-topology.c
@@ -0,0 +1,132 @@
+/*
+ * CPU Topology
+ *
+ * Copyright IBM Corp. 2022

The Copyright tag is different in the .h file.

OK, I change this to be like in the header file it seems to be the most used 
format.


+ * Author(s): Pierre Morel <pmorel@linux.ibm.com>
+
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/error-report.h"
+#include "hw/sysbus.h"
+#include "hw/qdev-properties.h"
+#include "hw/boards.h"
+#include "qemu/typedefs.h"
+#include "target/s390x/cpu.h"
+#include "hw/s390x/s390-virtio-ccw.h"
+#include "hw/s390x/cpu-topology.h"
+
+S390Topology *s390_get_topology(void)
+{
+    static S390Topology *s390Topology;
+
+    if (!s390Topology) {
+        s390Topology = S390_CPU_TOPOLOGY(
+            object_resolve_path(TYPE_S390_CPU_TOPOLOGY, NULL));
+    }
+
+    return s390Topology;

I am not convinced this routine is useful. The s390Topology pointer
could be stored under the machine state I think. It wouldn't be a
problem when CPUs are hot plugged since we have access to the machine
in the hot plug handler.

OK, I add a pointer to the machine state that will be initialised during 
s390_init_topology()

LGTM.



For the stsi call, 'struct ArchCPU' probably lacks a back pointer to
the machine objects with which CPU interact. These are typically
interrupt controllers or this new s390Topology model. You could add
the pointer there or, better, under a generic 'void *opaque' attribute.

That said, what you did works fine. The modeling could be cleaner.

Yes. I think you are right and I add a opaque pointer to the topology.

As an example, you could look at PPC where the PowerPCCPU CPU model is
shared between two differents machine, a baremetal one PowerNV and the
para-virtual one pSeries/sPAPR. Look for :

   pnv_cpu_state(PowerPCCPU *cpu)
   spapr_cpu_state(PowerPCCPU *cpu)

the machine CPU state is stored under an opaque cpu->machine_data which is
specific to each machine. It doesn't have to be as complex on s390 since
we only have one type of z-machine. An opaque is a good idea still.

Thanks,

C.



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