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Re: [Qemu-devel] [RFC v2 4/8] QAPI: new QMP command option "without-bql"
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [RFC v2 4/8] QAPI: new QMP command option "without-bql" |
Date: |
Mon, 28 Aug 2017 16:26:08 +0800 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Fri, Aug 25, 2017 at 10:06:27AM +0100, Dr. David Alan Gilbert wrote:
> * Peter Xu (address@hidden) wrote:
> > 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?
>
> It needs to be docuemnted for QMP users as well so that those developing
> management code know what's safe.
I see. What's the corresponding QMP documentation I should touch up?
>
> > 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)
>
> 'lock free' might be better?
I'm ok with it. But would the word "lock" too general?
--
Peter Xu
[Qemu-devel] [RFC v2 6/8] migration: qmp: migrate_incoming don't need BQL, Peter Xu, 2017/08/23
[Qemu-devel] [RFC v2 7/8] migration: hmp: migrate_incoming don't need BQL, Peter Xu, 2017/08/23
[Qemu-devel] [RFC v2 8/8] migration: add incoming mgmt lock, Peter Xu, 2017/08/23
Re: [Qemu-devel] [RFC v2 0/8] monitor: allow per-monitor thread, Daniel P. Berrange, 2017/08/29