From ff6a3c436c561a73b00e8dbe4b5c8dc52ecfda40 Mon Sep 17 00:00:00 2001
From: David Gibson <dgibson@redhat.com>
Date: Fri, 19 Jan 2018 04:04:55 +0100
Subject: [PATCH 15/21] ppc: Change Power9 compat table to support at most 8
threads/core
RH-Author: David Gibson <dgibson@redhat.com>
Message-id: <20180119040458.5629-2-dgibson@redhat.com>
Patchwork-id: 78675
O-Subject: [RHEL-7.5 qemu-kvm-rhev PATCH 1/4] ppc: Change Power9 compat table to support at most 8 threads/core
Bugzilla: 1529243
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
From: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
Increases the max smt mode to 8 for Power9. That's because KVM supports
smt emulation in this platform so QEMU should allow users to use it as
well.
Today if we try to pass -smp ...,threads=8, QEMU will silently truncate
it to smt4 mode and may cause a crash if we try to perform a cpu
hotplug.
Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
[dwg: Added an explanatory comment]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
(cherry picked from commit 03ee51d3548f5f553a3089f466483c1c6d5c666b)
Signed-off-by: David Gibson <dgibson@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
target/ppc/compat.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/target/ppc/compat.c b/target/ppc/compat.c
index 2d95434..94ff14a 100644
--- a/target/ppc/compat.c
+++ b/target/ppc/compat.c
@@ -73,7 +73,14 @@ static const CompatInfo compat_table[] = {
.pvr = CPU_POWERPC_LOGICAL_3_00,
.pcr = PCR_COMPAT_3_00,
.pcr_level = PCR_COMPAT_3_00,
- .max_threads = 4,
+ /*
+ * POWER9 hardware only supports 4 threads / core, but this
+ * limit is for guests. We need to support 8 vthreads/vcore
+ * on POWER9 for POWER8 compatibility guests, and it's very
+ * confusing if half of the threads disappear from the guest
+ * if it announces it's POWER9 aware at CAS time.
+ */
+ .max_threads = 8,
},
};
--
1.8.3.1