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.
--
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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