Re: [Qemu-devel] [RFC v2 4/8] QAPI: new QMP command option "without-bql"

[Peter Xu]

On Wed, Aug 23, 2017 at 06:44:12PM +0100, Dr. David Alan Gilbert wrote:

[...]

> > +Most of the commands require the Big QEMU Lock (BQL) be held during
> > +execution.  However, there is a small subset of the commands that may
> > +not really need BQL at all.  To mark out this kind of commands, we can
> > +specify "without-bql" to "true".  This parameter is only a hint for
> > +internal QMP implementation to provide possiblility to allow commands
> > +be run in parallel, or reduce the contention of the lock.  Users of QMP
> > +should not really be aware of such information.
> 
> Well, I think users of these commands might select them specifically
> because they know that they won't block.  Those who care about latency might
> look to use commands that don't take the lock because of a reduced
> effect on the performance as well.

What would be the best way to tell user?  I think again this should
mostly for HMP only, right?

Maybe we can add a new command to list these lock-free commands.  Or,
I can dump something in "help" and "help info" like:

(qemu) help migrate_incoming
migrate_incoming uri -- Continue an incoming migration from an -incoming defer 
(BQL-less)

-- 
Peter Xu