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