Re: [Qemu-devel] [PATCH 09/10] Exit loop if we have been there too long

[Anthony Liguori]

On 11/23/2010 05:03 PM, Juan Quintela wrote:
From: Juan Quintela<quint...@trasno.org>
cheking each 64 pages is a random magic number as good as any other.
We don't want to test too many times, but on the other hand,
qemu_get_clock_ns() is not so expensive either.

Signed-off-by: Juan Quintela<quint...@trasno.org>
Signed-off-by: Juan Quintela<quint...@redhat.com>
   

This is just introducing a future problem.

BufferedFile should hit the qemu_file_rate_limit check when the socket 
buffer gets filled up.  Are you claiming that the problem is due to 
trying to send a large number of zero pages?  Is this purely synthetic 
because you're testing an utilized large memory guest?

Regards,

Anthony Liguori

---
  arch_init.c |   16 ++++++++++++++++
  1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index d32aaae..b463798 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -40,6 +40,7 @@
  #include "net.h"
  #include "gdbstub.h"
  #include "hw/smbios.h"
+#include "buffered_file.h"

  #ifdef TARGET_SPARC
  int graphic_width = 1024;
@@ -218,6 +219,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
void *opaque)
      uint64_t bytes_transferred_last;
      uint64_t t0;
      double bwidth = 0;
+    int i;

      if (stage<  0) {
          cpu_physical_memory_set_dirty_tracking(0);
@@ -261,6 +263,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
void *opaque)
      bytes_transferred_last = bytes_transferred;
      t0 = qemu_get_clock_ns(rt_clock);

+    i = 0;
      while (!qemu_file_rate_limit(f)) {
          int bytes_sent;

@@ -269,6 +272,19 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
void *opaque)
          if (bytes_sent == 0) { /* no more blocks */
              break;
          }
+       /* we want to check in the 1st loop, just in case it was the 1st time
+           and we had to sync the dirty bitmap.
+           qemu_get_clock_ns() is a bit expensive, so we only check each some
+           iterations
+       */
+        if ((i&  63) == 0) {
+            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - t0) / 1000000;
+            if (t1>  buffered_file_interval/2) {
+                printf("big delay %ld milliseconds, %d iterations\n", t1, i);
+               break;
+           }
+       }
+        i++;
      }

      t0 = qemu_get_clock_ns(rt_clock) - t0;