* David Gibson (da...@gibson.dropbear.id.au) wrote: > On Fri, Oct 18, 2019 at 10:43:52AM +0100, Dr. David Alan Gilbert wrote: > > * Laurent Vivier (lviv...@redhat.com) wrote: > > > On 18/10/2019 10:16, Dr. David Alan Gilbert wrote: > > > > * Scott Cheloha (chel...@linux.vnet.ibm.com) wrote: > > > >> savevm_state's SaveStateEntry TAILQ is a priority queue. Priority > > > >> sorting is maintained by searching from head to tail for a suitable > > > >> insertion spot. Insertion is thus an O(n) operation. > > > >> > > > >> If we instead keep track of the head of each priority's subqueue > > > >> within that larger queue we can reduce this operation to O(1) time. > > > >> > > > >> savevm_state_handler_remove() becomes slightly more complex to > > > >> accomodate these gains: we need to replace the head of a priority's > > > >> subqueue when removing it. > > > >> > > > >> With O(1) insertion, booting VMs with many SaveStateEntry objects is > > > >> more plausible. For example, a ppc64 VM with maxmem=8T has 40000 such > > > >> objects to insert. > > > > > > > > Separate from reviewing this patch, I'd like to understand why you've > > > > got 40000 objects. This feels very very wrong and is likely to cause > > > > problems to random other bits of qemu as well. > > > > > > I think the 40000 objects are the "dr-connectors" that are used to plug > > > peripherals (memory, pci card, cpus, ...). > > > > Yes, Scott confirmed that in the reply to the previous version. > > IMHO nothing in qemu is designed to deal with that many devices/objects > > - I'm sure that something other than the migration code is going to > > get upset. > > It kind of did. Particularly when there was n^2 and n^3 cubed > behaviour in the property stuff we had some ludicrously long startup > times (hours) with large maxmem values. > > Fwiw, the DRCs for PCI slots, DRCs and PHBs aren't really a problem. > The problem is the memory DRCs, there's one for each LMB - each 256MiB > chunk of memory (or possible memory). > > > Is perhaps the structure wrong somewhere - should there be a single DRC > > device that knows about all DRCs? > > Maybe. The tricky bit is how to get there from here without breaking > migration or something else along the way.
Switch on the next machine type version - it doesn't matter if migration is incompatible then. Without knowing anything about the innards of DRCs, I suggest a DRCMulti that takes a parameter and represents 'n' DRCs at consecutive chunks of memory. Then use one DRCMulti for each RAMBlock or DIMM or other convenient sized thing. Dave > -- > 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 -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
