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From 689db60fc3f20c8aea0d5f382eb7d4de87e6bb3f 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 04:04:57 +0100
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Subject: [PATCH 17/21] spapr: Allow some cases where we can't set VSMT mode in
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the kernel
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RH-Author: David Gibson <dgibson@redhat.com>
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Message-id: <20180119040458.5629-4-dgibson@redhat.com>
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Patchwork-id: 78678
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O-Subject: [RHEL-7.5 qemu-kvm-rhev PATCH 3/4] spapr: Allow some cases where we can't set VSMT mode in the kernel
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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: David Gibson <david@gibson.dropbear.id.au>
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At present if we require a vsmt mode that's not equal to the kernel's
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default, and the kernel doesn't let us change it (e.g. because it's an old
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kernel without support) then we always fail.
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But in fact we can cope with the kernel having a different vsmt as long as
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a) it's >= the actual number of vthreads/vcore (so that guest threads
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that are supposed to be on the same core act like it)
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b) it's a submultiple of the requested vsmt mode (so that guest threads
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spaced by the vsmt value will act like they're on different cores)
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Allowing this case gives us a bit more freedom to adjust the vsmt behaviour
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without breaking existing cases.
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Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
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Reviewed-by: Laurent Vivier <lvivier@redhat.com>
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Tested-by: Greg Kurz <groug@kaod.org>
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Reviewed-by: Greg Kurz <groug@kaod.org>
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(cherry picked from commit 1f20f2e0ee61d91abff4e86ed1cda1b5244647d3)
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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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hw/ppc/spapr.c | 26 +++++++++++++++++++-------
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1 file changed, 19 insertions(+), 7 deletions(-)
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diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
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index 5233366..1086b5a 100644
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--- a/hw/ppc/spapr.c
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+++ b/hw/ppc/spapr.c
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@@ -2263,17 +2263,29 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp)
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if (kvm_enabled() && (spapr->vsmt != kvm_smt)) {
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ret = kvmppc_set_smt_threads(spapr->vsmt);
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if (ret) {
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+ /* Looks like KVM isn't able to change VSMT mode */
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error_setg(&local_err,
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"Failed to set KVM's VSMT mode to %d (errno %d)",
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spapr->vsmt, ret);
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- if (!vsmt_user) {
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- error_append_hint(&local_err, "On PPC, a VM with %d threads/"
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- "core on a host with %d threads/core requires "
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- " the use of VSMT mode %d.\n",
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- smp_threads, kvm_smt, spapr->vsmt);
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+ /* We can live with that if the default one is big enough
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+ * for the number of threads, and a submultiple of the one
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+ * we want. In this case we'll waste some vcpu ids, but
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+ * behaviour will be correct */
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+ if ((kvm_smt >= smp_threads) && ((spapr->vsmt % kvm_smt) == 0)) {
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+ warn_report_err(local_err);
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+ local_err = NULL;
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+ goto out;
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+ } else {
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+ if (!vsmt_user) {
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+ error_append_hint(&local_err,
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+ "On PPC, a VM with %d threads/core"
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+ " on a host with %d threads/core"
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+ " requires the use of VSMT mode %d.\n",
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+ smp_threads, kvm_smt, spapr->vsmt);
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+ }
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+ kvmppc_hint_smt_possible(&local_err);
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+ goto out;
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}
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- kvmppc_hint_smt_possible(&local_err);
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- goto out;
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}
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}
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/* else TCG: nothing to do currently */
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--
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1.8.3.1
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