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[21/26] stream: fix ratelimiting corner case

Message ID 1334232076-19018-22-git-send-email-pbonzini@redhat.com
State New
Headers show

Commit Message

Paolo Bonzini April 12, 2012, 12:01 p.m. UTC 
This fixes inability to make progress in streaming if the quota
is set to less than the amount of data that an I/O operation has
to write.

In this case, limit->dispatched + n will always be above the
quota and, due to the "goto retry" to recheck cancellation and
allocation, streaming will livelock.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/stream.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
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Patch

diff --git a/block/stream.c b/block/stream.c
index 2b492d5..b76104c 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -33,19 +33,19 @@  typedef struct {
 
 static int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
 {
-    int64_t delay_ns = 0;
     int64_t now = qemu_get_clock_ns(rt_clock);
 
     if (limit->next_slice_time < now) {
         limit->next_slice_time = now + SLICE_TIME;
         limit->dispatched = 0;
     }
-    if (limit->dispatched + n > limit->slice_quota) {
-        delay_ns = limit->next_slice_time - now;
-    } else {
+    if (limit->dispatched == 0 || limit->dispatched + n <= limit->slice_quota) {
         limit->dispatched += n;
+        return 0;
+    } else {
+        limit->dispatched = n;
+        return limit->next_slice_time - now;
     }
-    return delay_ns;
 }
 
 static void ratelimit_set_speed(RateLimit *limit, uint64_t speed)