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
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(_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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