On Tue, Sep 08, 2015 at 05:03:25PM -0500, Michael Roth wrote: > Quoting Michael Roth (2015-09-08 16:03:56) > > Quoting David Gibson (2015-09-07 20:22:50) > > > On Mon, Sep 07, 2015 at 11:37:04AM +0530, Bharata B Rao wrote: > > > > When drmgr is run in the guest to add a device for which device_add > > > > hasn't been issued in QEMU, configure-connector call fails. > > > > When configure-connector call fails, the guest would release (*) > > > > the previously acquired DRC by setting back the DRC isolation state > > > > to ISOLATED and allocation state to UNUSABLE. These calls will be issued > > > > only if get-sensor-state call returns PRESENT state. However currently > > > > for > > > > a logical DR, entity_sense() would unconditinally return UNUSABLE > > > > state only. This prevents any subsequent hotplug of the device with > > > > that DRC. > > > > This seems a little odd. I think we default to ALLOCATION_STATE_UNUSABLE > > for logical DR, and it's up the guest to transition to USABLE, which > > probably happens prior to the configure-connector calls. So I think the > > net effect of this fix is that guest will see these unallocated/unattached > > resources the same way they would a resource that was actually attached > > via device_add, and all we're really doing is working around the > > eventual configuration failure that that will lead to by pretending a > > resource was actually there. > > > > According to PAPR+ 2.7: > > > > 13.7.3.1 Acquire Logical Resource from Resource Pool: > > > > If the state is “unusable” the OS issues set-indicator (allocation-state, > > usable) to attempt to allocate the re- > > source. Similarly, if the state is “available for exchange” the OS issues > > set-indicator (allocation-state, ex- > > change) to attempt to allocate the resource, and if the state is > > “available for recovery” the OS issues > > set-indicator (allocation-state, recover) to attempt to allocate the > > resource. > > > > and > > > > 13.7 Logical Resource Dynamic Reconfiguration (LRDR): > > > > The OS may use the get-sensor-state RTAS call with the dr-entity-sense > > token to deter- > > mine if a given drc-index refers to a connector that is currently usable > > for DR operations. If the connector is not > > currently usable the return state is “DR entity unusable” (2). A > > set-indicator (isolation state) RTAS call to an unusable > > connector or (dr-indicator) to any logical resource connector results in a > > “No such indicator implemented” return sta- > > tus. > > > > So I think maybe the proper fix is to make sure that > > drc->set_indicator_state() fails with an error that indicates to RTAS to > > return NO_SENSOR (-3) for cases where we haven't attached a resource > > to the DRC via device_add. > > Patch incoming: > > spapr_drc: don't allow 'empty' DRCs to be unisolated > > applies to spapr-next but requires revert of this patch. > > Bharata, can you give it a spin with CPU hotplug and see if it fixes the > issue you hit? > > > > > Which also kind of re-opens the discussion of whether or not > > drc->set_indicator_state() should return RTAS errors directly. I'd > > still stray away from that for now but maybe if we get more cases > > like this it'll start becoming more practical. > > I'm starting to second-guess myself on this. I'm trying to maintain > separation between RTAS/DRC but result is a bit pathological. Feel free > to comment in the above patch.
To my mind the set_indicator path is pretty much inherently specific
to PAPR's weird way of doing things. For that reason I think it's
just going to be simplest for it to return PAPR defined errors -
i.e. RTAS errors.
The whole thing is so tied to PAPR, I don't think it makes sense to
try to use generic error codes for it. Trying to separate "DRC" error
codes from the RTAS codes they result in sounds like a translation
layer for no real gain.
> Just FYI: original author names appear to have gotten lost in recent
> spapr-next rebase.
Ah, thanks for catching that. Should be fixed now.
--
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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