* Markus Armbruster (arm...@redhat.com) wrote:
> Did this fall through the cracks?
>
> Denis Plotnikov <dplotni...@virtuozzo.com> writes:
>
> > Right now QMP and HMP monitors read 1 byte at a time from the socket, which
> > is very inefficient. With 100+ VMs on the host this easily reasults in
> > a lot of unnecessary system calls and CPU usage in the system.
>
> Yes, reading one byte at a time is awful. But QMP is control plane; I
> didn't expect it to impact system performance. How are you using QMP?
> Just curious, not actually opposed to improving QMP efficiency.
>
> > This patch changes the amount of data to read to 4096 bytes, which matches
> > buffer size on the channel level. Fortunately, monitor protocol is
> > synchronous right now thus we should not face side effects in reality.
> >
> > Signed-off-by: Denis V. Lunev <d...@openvz.org>
> > Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com>
> > ---
> > include/monitor/monitor.h | 2 +-
> > monitor.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
> > index c1b40a9cac..afa1ed34a4 100644
> > --- a/include/monitor/monitor.h
> > +++ b/include/monitor/monitor.h
> > @@ -14,7 +14,7 @@ extern __thread Monitor *cur_mon;
> > #define MONITOR_USE_CONTROL 0x04
> > #define MONITOR_USE_PRETTY 0x08
> >
> > -#define QMP_REQ_QUEUE_LEN_MAX 8
> > +#define QMP_REQ_QUEUE_LEN_MAX 4096
>
> This looks suspicious. It's a request count, not a byte count. Can you
> explain what led you to change it this way?
>
> >
> > bool monitor_cur_is_qmp(void);
> >
> > diff --git a/monitor.c b/monitor.c
> > index 4807bbe811..a08e020b61 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -4097,7 +4097,7 @@ static int monitor_can_read(void *opaque)
> > {
> > Monitor *mon = opaque;
> >
> > - return !atomic_mb_read(&mon->suspend_cnt);
> > + return !atomic_mb_read(&mon->suspend_cnt) ? 4096 : 0;
> > }
> >
> > /*
>
> The ramifications are not obvious to me. I think I need to (re-)examine
> how QMP reads input, with special consideration to its OOB feature.
Yeh that was the bit that worried me; I also wondered what happens with
monitor_suspend and things like fd passing; enough to make it
non-obvious to me.
Dave
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
