qemu-devel.nongnu.org archive mirror
 help / color / mirror / Atom feed
* [Qemu-devel] [PATCH] mainloop.c: Keep unlocking BQL during busy-wait spin-out
@ 2013-04-07  5:18 Peter Crosthwaite
  2013-04-15 13:08 ` Anthony Liguori
  0 siblings, 1 reply; 11+ messages in thread
From: Peter Crosthwaite @ 2013-04-07  5:18 UTC (permalink / raw)
  To: qemu-devel; +Cc: pbonzini, aliguori, Peter Crosthwaite

Modify Anthony's starvation detection logic to keep the BQL unlocked
until the starvation condition goes away. Otherwise the counter has to
count up to 1000 for each needed iteration until the busy-wait is
lifted.

Reset the counter back to zero once glib_pollfds_fill returns with a
non-zero timout, (indicating a return to normality). The 1000 iteration
wait now only happens once on the transition from normal operation to
busy-wait starvation.

Anthony's original patch fixed the serial paste bug, but this patch is
also needed to restore performance.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
---
 main-loop.c |   20 ++++++++++----------
 1 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/main-loop.c b/main-loop.c
index f46aece..93d2917 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -200,10 +200,13 @@ static int os_host_main_loop_wait(uint32_t timeout)
     /* If the I/O thread is very busy or we are incorrectly busy waiting in
      * the I/O thread, this can lead to starvation of the BQL such that the
      * VCPU threads never run.  To make sure we can detect the later case,
-     * print a message to the screen.  If we run into this condition, create
-     * a fake timeout in order to give the VCPU threads a chance to run.
+     * print a message to the screen.  If we run into this condition, unlock
+     * the BQL until a non-zero timout is given (indicating the starvation
+     * issue has gome away).
      */
-    if (spin_counter > MAX_MAIN_LOOP_SPIN) {
+    if (timeout > 0) {
+        spin_counter = 0;
+    } else if (spin_counter > MAX_MAIN_LOOP_SPIN) {
         static bool notified;
 
         if (!notified) {
@@ -212,21 +215,18 @@ static int os_host_main_loop_wait(uint32_t timeout)
                     MAX_MAIN_LOOP_SPIN);
             notified = true;
         }
-
-        timeout = 1;
     }
 
-    if (timeout > 0) {
-        spin_counter = 0;
+    if (timeout > 0 || spin_counter > MAX_MAIN_LOOP_SPIN) {
         qemu_mutex_unlock_iothread();
-    } else {
-        spin_counter++;
     }
 
     ret = g_poll((GPollFD *)gpollfds->data, gpollfds->len, timeout);
 
-    if (timeout > 0) {
+    if (timeout > 0 || spin_counter > MAX_MAIN_LOOP_SPIN) {
         qemu_mutex_lock_iothread();
+    } else {
+        spin_counter++;
     }
 
     glib_pollfds_poll();
-- 
1.7.0.4

^ permalink raw reply related	[flat|nested] 11+ messages in thread
end of thread, other threads:[~2013-04-29 11:15 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2013-04-07  5:18 [Qemu-devel] [PATCH] mainloop.c: Keep unlocking BQL during busy-wait spin-out Peter Crosthwaite
2013-04-15 13:08 ` Anthony Liguori
2013-04-15 13:13   ` Paolo Bonzini
2013-04-15 14:39     ` Anthony Liguori
2013-04-18 14:22   ` Peter Lieven
2013-04-18 14:35     ` Peter Crosthwaite
2013-04-19  7:01       ` Peter Lieven
2013-04-21 14:21         ` Peter Crosthwaite
2013-04-22  8:18           ` Peter Lieven
2013-04-29 11:15           ` Peter Lieven
2013-04-18 14:33   ` Peter Crosthwaite

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).