* Scott Cheloha (chel...@linux.vnet.ibm.com) wrote: > On Mon, Oct 21, 2019 at 09:14:44AM +0100, Dr. David Alan Gilbert wrote: > > * 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. > > 1mo bump. > > Is there anything I need to do with this patch in particular to make it > suitable > for merging?
Apologies for the delay; hopefully this will go in one of the pulls just after the tree opens again. Please please try and work on reducing the number of objects somehow - while this migration fix is a useful short term fix, and not too invasive; having that many objects around qemu is a really really bad idea so needs fixing properly. Dave > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
