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Re: [Qemu-devel] [PATCH] monitor: increase amount of data for monitor to
Re: [Qemu-devel] [PATCH] monitor: increase amount of data for monitor to read
Wed, 03 Jul 2019 08:36:53 +0200
Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)
Did this fall through the cracks?
Denis Plotnikov <address@hidden> 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 <address@hidden>
> Signed-off-by: Denis Plotnikov <address@hidden>
> 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.
- Re: [Qemu-devel] [PATCH] monitor: increase amount of data for monitor to read,
Markus Armbruster <=