From ff6a3c436c561a73b00e8dbe4b5c8dc52ecfda40 Mon Sep 17 00:00:00 2001 From: David Gibson 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 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 RH-Acked-by: Laurent Vivier RH-Acked-by: Miroslav Rezanina From: Jose Ricardo Ziviani 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 [dwg: Added an explanatory comment] Signed-off-by: David Gibson (cherry picked from commit 03ee51d3548f5f553a3089f466483c1c6d5c666b) Signed-off-by: David Gibson Signed-off-by: Miroslav Rezanina --- 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