Re: [Qemu-devel] [RFC PATCH v4 2/5] ramlist mutex

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/19/2011 08:20 AM, Umesh Deshpande wrote:
> Or, is it okay to convert all the ramblock list traversals in exec.c
> (under iothread) to mru traversals, and probably it makes sense as the
> original list was also maintained in the mru order, whereas the sequence
> of blocks doesn't matter for the migration code. This way we don't have
> to acquire the mutex for block list traversals.

I'm not sure... as I said, the MRU list is on a fast path and 
restricting it to that fast path keeps us honest.  Also, the non-MRU 
list is almost never accessed outside the migration thread, so the mutex 
shouldn't be heavily contended anyway.  You can also think about (not 
too clever) ways to keep the mutex unlocked while not doing ram_save_live.

BTW, actually the migration code tries to migrate the largest blocks 
first (because usually all the blocks after the first are small and 
easily migrated during the _complete pass), so the order does somewhat 
matter for migration.

Paolo