libxl_wait_for_memory_target: wait for 2 sec at a time

Use a 2 sec sleep time in the loop to allow the guest to release a
decent amount of memory in an iteration (empirical tests show ballooning
speed to be 512MB/sec or recent boxes).

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Mike Latimer <mlatimer@suse.com>
Tested-by: Mike Latimer <mlatimer@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl.c

@@ -4970,7 +4970,7 @@ int libxl_wait_for_memory_target(libxl_ctx *ctx, uint32_t domid, int wait_secs)
     prev_memkb = UINT64_MAX;
 
     do {
-        sleep(1);
+        sleep(2);
 
         libxl_dominfo_dispose(&info);
         libxl_dominfo_init(&info);
@@ -4986,7 +4986,7 @@ int libxl_wait_for_memory_target(libxl_ctx *ctx, uint32_t domid, int wait_secs)
             goto out;
         }
         else if (current_memkb == prev_memkb)
-            wait_secs--;
+            wait_secs -= 2;
         /* if current_memkb < prev_memkb loop for free as progress has
          * been made */