On Fri, May 12, 2017 at 04:54:57PM -0300, Daniel Henrique Barboza wrote:
>
>
> On 05/12/2017 03:12 AM, David Gibson wrote:
> > 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 <danie...@linux.vnet.ibm.com>
> > 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.
>
> Just had an idea that I think it's in the line of what you're suggesting.
> Given
> that the information we need is only created in the spapr_del_lmbs
> (as per patch 1), we can use the absence of this information in the
> release callback as a sort of a flag, an indication that a migration got
> in the way and we need to reconstruct the nr_lmbs states again, using
> the same scanning function I've used in v8.
>
> The flow would be like this (considering the changes in the
> previous 3 patches so far):
>
> ------------
>
> /* Callback to be called during DRC release. */
> void spapr_lmb_release(DeviceState *dev)
> {
> HotplugHandler *hotplug_ctrl;
>
> uint64_t addr = spapr_dimm_get_address(PC_DIMM(dev));
> sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
> sPAPRDIMMState *ds = spapr_pending_dimm_unplugs_find(spapr, addr);
>
> // no DIMM state found in spapr - re-create it to find out how may LMBs
> are left
> if (ds == NULL) {
> uint32 nr_lmbs = ***call_scanning_LMB_DRCs_function(dev)***
> // recreate the sPAPRDIMMState element and add it back to spapr
> }
>
> ( resume callback as usual )
>
> -----------
Yes, the above seems like a reasonable plan.
> Is this approach be adequate? Another alternative would be to use another
> way of detecting if an LMB unplug is happening and, if positive, do the same
> process in the post_load(). In this case I'll need to take a look in the
> code and
> see how we can detect an ongoing unplug besides what I've said above.
You could, but I think the lazy approach above is preferable.
>
> Thanks,
>
>
> Daniel
>
> >
> > > ---
> > > 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
signature.asc
Description: PGP signature
