Re: [Qemu-devel] [PATCH v5 3/4] monitor: more comments on lock-free fleids/funcs

[Peter Xu <peterx@redhat.com>]

On Thu, May 17, 2018 at 02:46:36PM +0200, Markus Armbruster wrote:
> Peter Xu <peterx@redhat.com> writes:
> 
> > Add some explicit comment for both Readline and cpu_set/cpu_get helpers
> > that they do not need the mon_lock protection.
> 
> Appreciated!
> 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  monitor.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/monitor.c b/monitor.c
> > index d6c3c08932..ae5bca9d7c 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -207,7 +207,7 @@ struct Monitor {
> >      int suspend_cnt;            /* Needs to be accessed atomically */
> >      bool skip_flush;
> >      bool use_io_thr;
> > -    ReadLineState *rs;
> > +    ReadLineState *rs;   /* Only used in parser, so no lock needed. */
> 
> Pardon the ignorant question: why does "only used in parser" imply "no
> lock needed"?

Since even if the monitors can be run in multiple threads now, the
monitor parser of a specific Monitor will still only be run in either
the main thread or the monitor iothread.  My fault to be unclear on
the comment.  Maybe this one is better:

  It is only used in parser, and the parser of a monitor will only be
  run either in main thread or monitor IOThread but never both, so no
  lock is needed when accessing ReadLineState.

> 
> >      MonitorQMP qmp;
> >      gchar *mon_cpu_path;
> >      BlockCompletionFunc *password_completion_cb;
> > @@ -1313,7 +1313,7 @@ void qmp_qmp_capabilities(bool has_enable, QMPCapabilityList *enable,
> >      cur_mon->qmp.commands = &qmp_commands;
> >  }
> >  
> > -/* set the current CPU defined by the user */
> > +/* set the current CPU defined by the user.  BQL needed. */
> 
> It's okay to start a comment containing a phrase with a lower case
> letter, but you're turning this one into two sentences, and sentences
> start in upper case.  Can touch up on commit.
> 
> "BQL needed" is okay, just a bit terse; I'd write "Caller must hold
> BQL".  Could change that, too.

I'll do that.

> 
> >  int monitor_set_cpu(int cpu_index)
> >  {
> >      CPUState *cpu;
> > @@ -1327,6 +1327,7 @@ int monitor_set_cpu(int cpu_index)
> >      return 0;
> >  }
> >  
> > +/* BQL neeeded. */
> 
> Likewise.

Will do.  Thanks,

-- 
Peter Xu