We ignore silently the value of smp_threads when we set
the default VSMT value, and if smp_threads is greater than VSMT
kernel is going into trouble later.
Fixes: 8904e5a750
("spapr: Adjust default VSMT value for better migration compatibility")
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
Notes:
v2: display a specific error message when the default VSMT is used
fix subject
hw/ppc/spapr.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 32a876be56..11de276cd5 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2311,6 +2311,12 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp)
* overwhelmingly common case in production systems.
*/
spapr->vsmt = 8;
+ if (spapr->vsmt < smp_threads) {
+ error_setg(&local_err, "Cannot support %d threads/core"
+ " because it must be <= to default VSMT mode (%d)",
+ smp_threads, spapr->vsmt);
+ goto out;
+ }
}
/* KVM: If necessary, set the SMT mode: */
--
2.14.3
On Thu, 8 Feb 2018 10:42:41 +0100 Laurent Vivier <lvivier@redhat.com> wrote: > We ignore silently the value of smp_threads when we set > the default VSMT value, and if smp_threads is greater than VSMT > kernel is going into trouble later. > > Fixes: 8904e5a750 > ("spapr: Adjust default VSMT value for better migration compatibility") > > Signed-off-by: Laurent Vivier <lvivier@redhat.com> > --- > Reviewed-by: Greg Kurz <groug@kaod.org> > Notes: > v2: display a specific error message when the default VSMT is used > fix subject > > hw/ppc/spapr.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > index 32a876be56..11de276cd5 100644 > --- a/hw/ppc/spapr.c > +++ b/hw/ppc/spapr.c > @@ -2311,6 +2311,12 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp) > * overwhelmingly common case in production systems. > */ > spapr->vsmt = 8; > + if (spapr->vsmt < smp_threads) { > + error_setg(&local_err, "Cannot support %d threads/core" > + " because it must be <= to default VSMT mode (%d)", > + smp_threads, spapr->vsmt); > + goto out; > + } > } > > /* KVM: If necessary, set the SMT mode: */
On Thu, Feb 08, 2018 at 10:42:41AM +0100, Laurent Vivier wrote: > We ignore silently the value of smp_threads when we set > the default VSMT value, and if smp_threads is greater than VSMT > kernel is going into trouble later. > > Fixes: 8904e5a750 > ("spapr: Adjust default VSMT value for better migration compatibility") > > Signed-off-by: Laurent Vivier <lvivier@redhat.com> I don't think this is quite the rigth appoach. Instead, I think we want: spapr->vsmt = MAX(8, smp_threads); The real point of 8904e5a750 was to replace the host-derived kvm_smt with a fixed value (8). I only removed the MAX, because I mistakenly thought that checks elsewhere would prevent smp_threads > 8. > --- > > Notes: > v2: display a specific error message when the default VSMT is used > fix subject > > hw/ppc/spapr.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > index 32a876be56..11de276cd5 100644 > --- a/hw/ppc/spapr.c > +++ b/hw/ppc/spapr.c > @@ -2311,6 +2311,12 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp) > * overwhelmingly common case in production systems. > */ > spapr->vsmt = 8; > + if (spapr->vsmt < smp_threads) { > + error_setg(&local_err, "Cannot support %d threads/core" > + " because it must be <= to default VSMT mode (%d)", > + smp_threads, spapr->vsmt); > + goto out; > + } > } > > /* KVM: If necessary, set the SMT mode: */ -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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