Re: [PATCH v2 2/2] monitor: increase amount of data for monitor to read

[Vladimir Sementsov-Ogievskiy]

23.11.2020 18:44, Andrey Shinkevich wrote:
> QMP and HMP monitors read one byte at a time from the socket or stdin,
> which is very inefficient. With 100+ VMs on the host, this results in
> multiple extra system calls and CPU overuse.
> This patch increases the amount of read data up to 4096 bytes that fits
> the buffer size on the channel level.
> A JSON little parser is introduced to throttle QMP commands read from
> the buffer so that incoming requests do not overflow the monitor input
> queue.
>
> Suggested-by: Denis V. Lunev<den@openvz.org>
> Signed-off-by: Andrey Shinkevich<andrey.shinkevich@virtuozzo.com>


Can't we just increase qmp queue instead? It seems a lot simpler:

diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
index 348bfad3d5..7e721eee3f 100644
--- a/include/monitor/monitor.h
+++ b/include/monitor/monitor.h
@@ -8,7 +8,7 @@
 typedef struct MonitorHMP MonitorHMP;
 typedef struct MonitorOptions MonitorOptions;
 
-#define QMP_REQ_QUEUE_LEN_MAX 8
+#define QMP_REQ_QUEUE_LEN_MAX 4096
 
 extern QemuOptsList qemu_mon_opts;
 
diff --git a/monitor/monitor.c b/monitor/monitor.c
index 84222cd130..1588f00306 100644
--- a/monitor/monitor.c
+++ b/monitor/monitor.c
@@ -566,7 +566,7 @@ int monitor_can_read(void *opaque)
 {
     Monitor *mon = opaque;
 
-    return !qatomic_mb_read(&mon->suspend_cnt);
+    return !qatomic_mb_read(&mon->suspend_cnt) ? 4096 : 0;
 }


- with this patch tests pass and performance is even better.


--
Best regards,
Vladimir