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

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>,
	qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org, marcandre.lureau@redhat.com,
	pbonzini@redhat.com, kwolf@redhat.com, mreitz@redhat.com,
	armbru@redhat.com, dgilbert@redhat.com, den@openvz.org
Subject: Re: [PATCH v2 2/2] monitor: increase amount of data for monitor to read
Date: Tue, 24 Nov 2020 14:03:13 +0300	[thread overview]
Message-ID: <edb0cc5c-62e6-7277-59ae-e49e721fa596@virtuozzo.com> (raw)
In-Reply-To: <1606146274-246154-3-git-send-email-andrey.shinkevich@virtuozzo.com>

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

