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Re: [Qemu-ppc] [PATCH] pseries: Restore support for total vcpus not a mu
From: |
Greg Kurz |
Subject: |
Re: [Qemu-ppc] [PATCH] pseries: Restore support for total vcpus not a multiple of threads-per-core for old machine types |
Date: |
Tue, 23 May 2017 09:16:31 +0200 |
On Tue, 23 May 2017 16:36:45 +1000
David Gibson <address@hidden> wrote:
> As of pseries-2.7 and later, we require the total number of guest vcpus to
> be a multiple of the threads-per-core. pseries-2.6 and earlier machine
> types, however, are supposed to allow this for the sake of migration from
> old qemu versions which allowed this.
>
> Unfortunately, 8149e29 "pseries: Enforce homogeneous threads-per-core"
> broke this by not considering the old machine type case. This fixes it by
> only applying the check when the machine type supports hotpluggable cpus.
> By not-entirely-coincidence, that corresponds to the same time when we
> started enforcing total threads being a multiple of threads-per-core.
>
> Fixes: 8149e2992f7811355cc34721b79d69d1a3a667dd
>
> Signed-off-by: David Gibson <address@hidden>
> ---
Reviewed-by: Greg Kurz <address@hidden>
and
Tested-by: Greg Kurz <address@hidden>
> hw/ppc/spapr.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index c92d269..bcb0e18 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2863,7 +2863,13 @@ static void spapr_core_pre_plug(HotplugHandler
> *hotplug_dev, DeviceState *dev,
> goto out;
> }
>
> - if (cc->nr_threads != smp_threads) {
> + /*
> + * In general we should have homogeneous threads-per-core, but old
> + * (pre hotplug support) machine types allow the last core to have
> + * reduced threads as a compatibility hack for when we allowed
> + * total vcpus not a multiple of threads-per-core.
> + */
> + if (mc->has_hotpluggable_cpus && (cc->nr_threads != smp_threads)) {
> error_setg(errp, "invalid nr-threads %d, must be %d",
> cc->nr_threads, smp_threads);
> return;
pgpzhiPLgnMUc.pgp
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