Re: [Qemu-devel] [PATCH v9 4/6] hw/ppc/spapr.c: migrate pending_dimm_unplugs of spapr state

[David Gibson]

On Fri, May 05, 2017 at 05:47:44PM -0300, Daniel Henrique Barboza wrote:
> To allow for a DIMM unplug event to resume its work if a migration
> occurs in the middle of it, this patch migrates the non-empty
> pending_dimm_unplugs QTAILQ that stores the DIMM information
> that the spapr_lmb_release() callback uses.
> 
> It was considered an apprach where the DIMM states would be restored
> on the post-_load after a migration. The problem is that there is
> no way of knowing, from the sPAPRMachineState, if a given DIMM is going
> through an unplug process and the callback needs the updated DIMM State.
> 
> We could migrate a flag indicating that there is an unplug event going
> on for a certain DIMM, fetching this information from the start of the
> spapr_del_lmbs call. But this would also require a scan on post_load to
> figure out how many nr_lmbs are left. At this point we can just
> migrate the nr_lmbs information as well, given that it is being calculated
> at spapr_del_lmbs already, and spare a scanning/discovery in the
> post-load. All that we need is inside the sPAPRDIMMState structure
> that is added to the pending_dimm_unplugs queue at the start of the
> spapr_del_lmbs, so it's convenient to just migrated this queue it if it's
> not empty.
> 
> Signed-off-by: Daniel Henrique Barboza <address@hidden>

NACK.

As I believe I suggested previously, you can reconstruct this state on
the receiving side by doing a full scan of the DIMM and LMB DRC states.

> ---
>  hw/ppc/spapr.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index e190eb9..30f0b7b 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1437,6 +1437,36 @@ static bool version_before_3(void *opaque, int 
> version_id)
>      return version_id < 3;
>  }
>  
> +static bool spapr_pending_dimm_unplugs_needed(void *opaque)
> +{
> +    sPAPRMachineState *spapr = (sPAPRMachineState *)opaque;
> +    return !QTAILQ_EMPTY(&spapr->pending_dimm_unplugs);
> +}
> +
> +static const VMStateDescription vmstate_spapr_dimmstate = {
> +    .name = "spapr_dimm_state",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(addr, sPAPRDIMMState),
> +        VMSTATE_UINT32(nr_lmbs, sPAPRDIMMState),
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
> +static const VMStateDescription vmstate_spapr_pending_dimm_unplugs = {
> +    .name = "spapr_pending_dimm_unplugs",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = spapr_pending_dimm_unplugs_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_QTAILQ_V(pending_dimm_unplugs, sPAPRMachineState, 1,
> +                         vmstate_spapr_dimmstate, sPAPRDIMMState,
> +                         next),
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
>  static bool spapr_ov5_cas_needed(void *opaque)
>  {
>      sPAPRMachineState *spapr = opaque;
> @@ -1535,6 +1565,7 @@ static const VMStateDescription vmstate_spapr = {
>      .subsections = (const VMStateDescription*[]) {
>          &vmstate_spapr_ov5_cas,
>          &vmstate_spapr_patb_entry,
> +        &vmstate_spapr_pending_dimm_unplugs,
>          NULL
>      }
>  };

-- 
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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