[RFC] Use cpu_get_icount as cpu_get_host_ticks fallback

Commit Message

Christopher Covington March 18, 2016, 8:56 p.m. UTC

The previous increment-on-read fallback didn't increment fast
enough for some versions of grub.

https://bugs.launchpad.net/qemu-linaro/+bug/893208

Signed-off-by: Christopher Covington <[e-mail]>
---
I unfortunately don't have the opportunity to fully test this right
now, but I'm sending it out nevertheless on the off chance that
someone else might.
---
 include/qemu/timer.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Patch

diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index d0946cb..60c6dd6 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -998,13 +998,12 @@  static inline int64_t cpu_get_host_ticks(void)
 }
 
 #else
-/* The host CPU doesn't have an easily accessible cycle counter.
-   Just return a monotonically increasing value.  This will be
-   totally wrong, but hopefully better than nothing.  */
+/* The host CPU doesn't have an easily accessible cycle counter, so just return
+   the instruction count. This may make the CPU look like it has an IPC of
+   exactly 1, but that shouldn't cause any functional problems. */
 static inline int64_t cpu_get_host_ticks (void)
 {
-    static int64_t ticks = 0;
-    return ticks++;
+    return cpu_get_icount();
 }
 #endif