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* [PATCH] monitor: Fix slow reading
@ 2019-11-22  9:23 Yury Kotov
  2019-11-22 10:23 ` Philippe Mathieu-Daudé
  2019-11-29  8:21 ` Markus Armbruster
  0 siblings, 2 replies; 7+ messages in thread
From: Yury Kotov @ 2019-11-22  9:23 UTC (permalink / raw)
  To: qemu-devel; +Cc: Markus Armbruster, yc-core, Dr. David Alan Gilbert

The monitor_can_read (as a callback of qemu_chr_fe_set_handlers)
should return size of buffer which monitor_qmp_read or monitor_read
can process.
Currently, monitor_can_read returns 1 as a result of logical not.
Thus, for each QMP command, len(QMD) iterations of the main loop
are required to handle a command.
In fact, these both functions can process any buffer size.
So, return 1024 as a reasonable size which is enough to process
the most QMP commands, but not too big to block the main loop for
a long time.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
---
 monitor/monitor.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/monitor/monitor.c b/monitor/monitor.c
index 12898b6448..cac3f39727 100644
--- a/monitor/monitor.c
+++ b/monitor/monitor.c
@@ -50,6 +50,13 @@ typedef struct {
     int64_t rate;       /* Minimum time (in ns) between two events */
 } MonitorQAPIEventConf;
 
+/*
+ * The maximum buffer size which the monitor can process in one iteration
+ * of the main loop. We don't want to block the loop for a long time
+ * because of JSON parser, so use a reasonable value.
+ */
+#define MONITOR_READ_LEN_MAX 1024
+
 /* Shared monitor I/O thread */
 IOThread *mon_iothread;
 
@@ -498,7 +505,7 @@ int monitor_can_read(void *opaque)
 {
     Monitor *mon = opaque;
 
-    return !atomic_mb_read(&mon->suspend_cnt);
+    return atomic_mb_read(&mon->suspend_cnt) ? 0 : MONITOR_READ_LEN_MAX;
 }
 
 void monitor_list_append(Monitor *mon)
-- 
2.24.0



^ permalink raw reply related	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2019-12-03  8:30 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-22  9:23 [PATCH] monitor: Fix slow reading Yury Kotov
2019-11-22 10:23 ` Philippe Mathieu-Daudé
2019-11-29  8:21 ` Markus Armbruster
2019-12-02 17:43   ` Yury Kotov
2019-12-02 20:49     ` Markus Armbruster
2019-12-03  7:40       ` Denis V. Lunev
2019-12-03  8:27       ` Yury Kotov

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